build-function

The way to describe and build simple functions using JSON

Motivation

I need to allow the end user to create some simple function using a JSON file (mostly math based functions), but without allowing them to access the global scope. This module allow them to declare and run functions, but in an enclosed environment provided by the developer.

Performance Notice

Functions built with this module are very slow, despite the fact that we pre-compile and cache every expression and statement. Use it only when performance is not an issue.

In This Guide

• CDN
• API
  • build
  • compileExp
  • compileStep
  • createEnv
  • findInEnv
  • setInEnv
• Expressions
  • literal Literal Expression
  • get Get Expression
  • set Set Expression
  • ternary Ternary Expression
  • oper Operation Expression
  • trans Transform Expression
  • func Function Expression
  • call Function Call Expression
  • spread Spread Expression
• Statements
  • let Variable Declaration Statement
  • if If Statement
  • for For Statement
  • break Break Statement
  • return Return Statement
  • try Try Statement
  • throw Throw Statement
• Steps
• Operations
• Transformations

CDN

jsDelivr

<script src="https://cdn.jsdelivr.net/npm/build-function@latest/dist/build.umd.js"></script>

for production...

<script src="https://cdn.jsdelivr.net/npm/build-function@latest/dist/build.umd.min.js"></script>

more options...

UNPKG

<script src="https://unpkg.com/build-function@latest/dist/build.umd.js"></script>

for production...

<script src="https://unpkg.com/build-function@latest/dist/build.umd.min.js"></script>

more options...

API

build

Creates a function from options using env as outer environment.

function build(
  options: BuildFunctionOptions,
  env?: Environment,
): Function;

interface BuildFunctionOptions {
  name?: string;
  params?: string | ParamDescriptor | Array<string | ParamDescriptor>;
  body?: Step | Step[];
}

arguments

• options

  Function options.

  • name (optional)

    A name for the function, if provided it will be registered to the environment so you can call the function recursively.

  • params (optional)

    see Function Expression for more information.

  • body (optional)

    see Function Expression for more information.

• env (optional)

  Outer environment for the function. see environment section for more information.

compileExp

Compiles an expression or array of expressions into a function or array of functions.

function compileExp(
  expression: Expression,
  cache: object,
  safeGet?: boolean,
): (env: Environment) => any;

function compileExp(
  expression: Array<Expression>,
  cache: object,
  safeGet?: boolean,
): Array<(env: Environment) => any>;

arguments

• expression

  Expression or array of Expressions to be compiled.

• cache

  Cache object.

• safeGet (optional)

  Whether or not to return undefined if id not found on a get expression. If safeGet is falsy get expression will throw if id not present in the environment.

compileStep

Compiles a step or array of steps into a function.

function compileStep(
  step: Step | Step[],
  cache: object,
  allowBreak?: boolean,
): (env: Environment) => StepResult;

arguments

• step

  Step or array of steps to be compiled.

• cache

  Cache object.

• allowBreak (optional)

  Whether or not to allow break statements.

createEnv

Creates a new environment with parent as parent environment.

function createEnv(
  parent: Environment | null,
  lib?: EnvironmentLib | null,
): Environment;

arguments

• parent

  Parent environment.

• lib

  Variables to be added to the newly created environment.

findInEnv

Searches for an id in an environment.

function findInEnv(
  env: Environment,
  id: string,
  topOnly?: boolean,
): EnvFound | void;

interface EnvFound {
  env: Environment;
  id: string;
}

arguments

• env

  The environment.

• id

  Variable id to search for.

• topOnly (optional)

  Whether or not to search the top level environment only. Otherwise it will keep searching every parent environment.

setInEnv

Sets a value into an environment.

function setInEnv(
  env: Environment,
  id: string,
  value: any,
): void;

arguments

• env

  The environment to set the variable.

• id

  The variable id.

• value

  The variable value.

Expressions

Literal Expression

It resolves to a literal expression.

syntax

interface LiteralExpression {
  type: "literal";
  value: any;
}

• type

  Always "literal", it's what identifies a literal expression from other expressions and statements.

• value

  Value to be used as literal when expression is evaluated. This value will be serialized using JSON.stringify and then reparsed using JSON.parse when expression is evaluated, it allows to resolve to a fresh object or array when expresion is evaluated.

example

{
  "type": "literal",
  "value": [1, 2]
}

... is equivalent to...

[1, 2]

Get Expression

Gets a value of the variable identified by the id from the current virtual environment. If the variable if not found, it will throw, unless it is inside a typeof trnsform operation.

syntax

interface GetExpression {
  type: "get";
  id: string;
}

• type

  Always "get", it's what identifies a get expression from other expressions and statements.

• id

  String representing the id to be used when expression is resolved.

  If the id is not present in the current virtual environment, it will throw.

example

{
  "type": "get",
  "id": "current"
}

... is equivalent to...

current

Set Expression

It sets a value to the variable identified by the id in the current virtual environment. If the variable has not been declared prevoiusly, it will throw. The expression will resolve to the value being set.

syntax

interface SetExpression {
  type: "set";
  id: string;
  value: Expression;
}

• type

  Always "set", it's what identifies a set expression from other expressions and statements.

• id

  String representing the id to be used when expression is resolved.

• value

  Expression resolving to a value to be assigned to the corresponding id in the current virtual environment.

example

{
  "type": "set",
  "id": "a",
  "value": {
    "type": "set",
    "id": "b",
    "value": {
      "type": "literal",
      "value": true
    }
  }
}

... is equivalent to...

a = b = true

Note that set expressions resolve to the value being set so they can be chained together.

Ternary Expression

It resolves to a ternary operation expression.

syntax

interface TernaryExpression {
  type: "ternary";
  condition: Expression;
  then: Expression;
  otherwise: Expression;
}

• type

  Always "ternary", it's what identifies a ternary expression from other expressions and statements.

• condition

  Expression which result will be used as condition for the ternary expression.

• then

  Expression which result will be used as resul for the ternary expression if condition is truthy.

• otherwise

  Expression which result will be used as resul for the ternary expression if condition is falsy.

example

{
  "type": "ternary",
  "condition": {
    "type": "get",
    "id": "value",
    "then": {
      "type": "literal",
      "value": "yes"
    },
    "otherwise": {
      "type": "literal",
      "value": "no"
    }
  }
}

... is equivalent to...

value ? "yes" : "no"

Operation Expression

It performs an operation between 2 or more operands, see operations for supported operators and information.

syntax

interface OperationExpression {
  type: "oper";
  oper: MultiTermOperator;
  exp: Expression[];
}

• type

  Always "oper", it's what identifies an operation expression from other expressions and statements.

• oper

  The operator to be used in the operation, see operations for more information.

• exp

  Array of expressions to be used in the operation, if less than 2 operators provided, it will throw at compile time.

example

{
  "type": "oper",
  "oper": "*",
  "exp": [
    {
      "type": "literal",
      "value": "15"
    },
    {
      "type": "oper",
      "oper": "+",
      "exp": [
        {
          "type": "get",
          "id": "value"
        },
        {
          "type": "literal",
          "value": 2
        },
        {
          "type": "literal",
          "value": 5
        }
      ]
    }
  ]
}

... is equivalent to...

15 * (value + 2 + 5)

Every operation expression acts like its operands has been grouped inside parentheses, so the order of operations doesn't apply.

Transform Expression

It performs a transform operation to another expression, see transformations for supported operators and information.

syntax

interface TransformExpression {
  type: "trans";
  oper: TransformOperator;
  exp: Expression;
}

• type

  Always "trans", it's what identifies a trnsform expression from other expressions and statements.

• oper

  The operator to be used in the operation, see transformations for more information.

• exp

  Expression which result will be transformed.

example

{
  "type": "trans",
  "oper": "typeof",
  "exp": {
    "type": "get",
    "id": "value"
  }
}

... is equivalent to...

typeof value

Function Expression

It represents a function expression.

syntax

interface FunctionExpression {
  type: "func";
  params?: string | ParamDescriptor | Array<string | ParamDescriptor>;
  body?: Step | Step[];
}

interface ParamDescriptor {
  id: string;
  type: "param" | "rest";
}

• type

  Always "func", it's what identifies a function expression from other expressions and statements.

• params (optional)

  String representing the the param id, object representing param id and type, or an array of them representing multiple parameters.

• body (optional)

  A step or array of steps to be executed when the function is called. See function steps for more information.

example

{
  "type": "func",
  "params": "obj",
  "body": {
    "type": "return",
    "value": {
      "type": "trans",
      "oper": "!",
      "exp": {
        "type": "get",
        "id": "obj"
      }
    }
  }
}

... is equivalent to...

function (obj) {
  return !obj;
}

Function Call Expression

It represents a function call result expression.

syntax

interface FunctionCallExpression {
  type: "call";
  func: Expression;
  args?: Expression | SpreadExpression | Array<Expression | SpreadExpression>;
}

• type

  Always "call", it's what identifies a function call expression from other expressions and statements.

• func

  Expression which resolves to a function to be called.

• args (optional)

  Expression, spread expression or array of them to be used as arguments to call the function.

example

{
  "type": "call",
  "func": {
    "type": "get",
    "id": "concat"
  },
  "args": [
    {
      "type": "literal",
      "value": "Hello "
    },
    {
      "type": "get",
      "id": "name"
    }
  ]
}

... is equivalent to...

concat("Hello ", name)

Spread Expression

It spreads the values of an array for a function call. Spread expressions only work on function call expressions, it will throw if used somewhere else.

syntax

interface SpreadExpression {
  type: "spread";
  exp: Expression;
}

• type

  Always "spread", it's what identifies a spread expression from other expressions and statements.

• exp

  Expression which resolves to an array to be spread.

example

{
  "type": "call",
  "func": {
    "type": "get",
    "id": "func"
  },
  "args": [
    {
      "type": "literal",
      "value": 100
    },
    {
      "type": "spread",
      "exp": {
        "type": "get",
        "id": "others"
      }
    }
  ]
}

... is equivalent to...

func(100, ...others)

Statements

let Statement

Declares variables into the current virtual environment.

syntax

interface LetStatement {
  type: "let";
  declare: string | DeclareWithValue | Array<string | DeclareWithValue>;
}

interface DeclareWithValue {
  id: string;
  value?: Expression;
}

• type

  Always "let", it's what identifies a let statement from other statements and expressions.

• declare

  An id, id-value-pair or array of them to be declared into the current virtual environment.

example

{
  "type": "let",
  "declare": [
    "a",
    {
      "id": "b"
    },
    {
      "id": "c",
      "value": 10
    }
  ]
}

... is equivalent to...

let a, b, c = 10;

if Statement

Declares an if statement.

syntax

interface IfStatement {
  type: "if";
  condition: Expression;
  then?: Step | Step[];
  otherwise?: Step | Step[];
}

• type

  Always "if", it's what identifies an if statement from other statements and expressions.

• condition

  Expression which result will be used as condition for the if statement.

• then (optional)

  A step or array of steps to be executed if condition resolves to a truthy value. See function steps for more information.

• otherwise (optional)

  A step or array of steps to be executed if condition resolves to a falsy value. See function steps for more information.

example

{
  "type": "if",
  "condition": {
    "type": "get",
    "id": "test"
  },
  "then": {
    "type": "call",
    "func": {
      "type": "get",
      "id": "func1"
    }
  },
  "otherwise": {
    "type": "call",
    "func": {
      "type": "get",
      "id": "func2"
    }
  }
}

... is equivalent to...

if (test) {
  func1();
} else {
  func2();
}

for Statement

Declares a for loop.

syntax

interface ForStatement {
  type: "for";
  target: Expression;
  index?: string;
  value?: string;
  body?: Step | Step[];
}

• type

  Always "for", it's what identifies a for statement from other statements and expressions.

• target

  Expression resolving to an array-like object, which length property will be used for the loop.

• index (optional)

  The id to be registered inside the loop body virtual environment containing the current iteration index, if not specified it won't be registered, the loop will still run.

• value (optional)

  The id to be registered inside the loop body virtual environment containing the current iteration value, if not specified it won't be registered, the loop will still run.

• body (optional)

  A step or array of steps to be executed for every iteration. See function steps for more information.

example

{
  "type": "for",
  "target": {
    "type": "get",
    "id": "array"
  },
  "index": "index",
  "value": "item",
  "body": {
    "type": "call",
    "func": {
      "type": "get",
      "id": "func"
    },
    "args": [
      {
        "type": "get",
        "id": "index"
      },
      {
        "type": "get",
        "id": "item"
      }
    ]
  }
}

... is equivalent to...

for (let i = 0; i < array.length; i++) {
  func(i, array[i]);
}

break Statement

Declares a break statement, it will throw at build time if used outside a loop.

syntax

interface BreakStatement {
  type: "break";
}

• type

  Always "break", it's what identifies a break statement from other statements and expressions.

return Statement

It represents a return statement.

syntax

interface ReturnStatement {
  type: "return";
  value: Expression;
}

• type

  Always "return", it's what identifies a return statement from other statements and expressions.

• value

  Expression which result will be used as return value.

example

{
  "type": "return",
  "value": {
    "type": "get",
    "id": "result"
  }
}

... is equivalent to...

return result;

try Statement

It represents a try statement.

syntax

interface TryStatement {
  type: "try";
  body?: Step | Step[];
  error?: string;
  catch?: Step | Step[];
}

• type

  Always "try", it's what identifies a try statement from other statements and expressions.

• body (optional)

  A step or array of steps to be executed inside try block.

• error (optional)

  The id to be registered inside the catch block virtual environment containing the error message, if not specified it won't be registered.

• catch (optional)

  A step or array of steps to be executed inside catch block.

  If error option provided you can access the error message using a get expression.

example

{
  "type": "try",
  "body": {
    "type": "call",
    "func": {
      "type": "get",
      "id": "test"
    },
    "args": [
      {
        "type": "get",
        "id": "a"
      },
      {
        "type": "get",
        "id": "b"
      }
    ]
  },
  "error": "err",
  "catch": {
    "type": "call",
    "func": {
      "type": "get",
      "id": "log"
    },
    "args": {
      "type": "get",
      "id": "err"
    }
  }
}

... is equivalent to...

try {
  test(a, b);
} catch (err) {
  log(err);
}

throw Statement

It represents a throw statement.

syntax

interface ThrowStatement {
  type: "throw";
  msg: string | Expression;
}

• type

  Always "throw", it's what identifies a throw statement from other statements and expressions.

• msg

  A string or Expression resolving to a string to be used as error message.

example

{
  "type": "throw",
  "msg": "Unknown Error"
}

... is equivalent to...

throw new Error("Unknown Error");

Steps

Any statement or expression is considered a step.

Operations

Multiterm operations are defined using the Operation Expression.

Supported Operators

+ Addition Operator

- Subtraction Operator

* Multiplication Operator

/ Division Operator

% Modulus Operator

** Exponentiation Operator

&& Logic AND Operator

|| Logic OR Operator

== Equal Operator

=== Strict equal Operator

!= Unequal Operator

!== Strict unequal Operator

< Less than Operator

<= Less than or equal Operator

> Greater than Operator

>= Greater than or equal Operator

& Bitwise AND Operator

| Bitwise OR Operator

^ Bitwise XOR Operator

<< Shift Left Operator

>> Shift Right Operator

>>> Unsigned Shift Right Operator

Transformations

Transformations are defined using the Transform Expression.

Supported Transform Operators

typeof Type Operator

! NOT Operator

!! To Boolean Operator

~ Bitwise NOT Operator

License

MIT © Manuel Fernández