@ucast/js
v3.0.4
Published
[email protected]:stalniy/ucast.git
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UCAST JavaScript
This package is a part of ucast ecosystem. It provides interpreter that can execute conditions AST in JavaScript against any JavaScript object.
Installation
npm i @ucast/js
# or
yarn add @ucast/js
# or
pnpm add @ucast/js
Getting Started
Interpret conditions AST
First of all, you need AST to interpret it. For the sake of an example, we will create it manually:
import { CompoundCondition, FieldCondition } from '@ucast/core';
import { interpret } from '@ucast/js';
// x > 5 && y < 10
const condition = new CompoundCondition('and', [
new FieldCondition('gt', 'x', 5),
new FieldCondition('lt', 'y', 10),
]);
interpret(condition, { x: 2, y: 1 }); // false
interpret(condition, { x: 6, y: 7 }); // true
The default interpret
function:
supports the next operators, implemented according to MongoDB query language:
eq
,ne
lt
,lte
gt
,gte
within
(the same asin
butin
is a reserved word in JavaScript),nin
all
regex
or
,nor
,and
,not
exists
size
mod
where
,elemMatch
supports dot notation to access nested object property values in conditions:
const condition = new FieldCondition('eq', 'address.street', 'some street'); interpret(condition, { address: { street: 'another street' } }); // false
compare values by strict equality, so variables that reference objects are equal only if they are references to the same object:
const address = { street: 'test' }; const condition = new FieldCondition('eq', 'address', address); interpret(condition, { address }) // true interpret(condition, { address: { street: 'test' } }) // false, objects are compared by strict equality
Custom interpreter
Sometimes you may want to reduce (or restrict) amount of supported operators (e.g., to utilize tree-shaking and reduce bundle size). To do this you can create a custom interpreter manually:
import { FieldCondition } from '@ucast/core';
import { createJsInterpreter, eq, lt, gt } from '@ucast/js';
// supports only $eq, $lt and $gt operators
const interpret = createJsInterpreter({ eq, lt, gt });
const condition = new FieldCondition('in', 'x', [1, 2]);
interpret(condition, { x: 1 }) // throws Error, `$in` is not supported
Custom object matching
You can also provide a custom get
or compare
function. So, you can implement custom logic to get object's property or to compare values. compare
is used everywhere equality or comparison is required (e.g., in $in
, $lt
, $gt
). This function must return 1
if a > b
, -1
if a < b
and 0
if a === b
.
Let's enhance our interpreter to support deep object comparison using [lodash]:
import isEqual from 'lodash/isEqual';
import { createJsInterpreter, allInterpreters, compare } from '@ucast/js';
const interpret = createJsInterpreter(allInterpreters, {
compare(a, b) {
if (typeof a === typeof b && typeof a === 'object' && isEqual(a, b)) {
return 0;
}
return compare(a, b);
}
});
const condition = new FieldCondition('eq', 'x', { active: true });
interpret(condition, { x: { active: true } }); // true
Custom Operator Interpreter
Any operator is just a function that accepts 3 parameters and returns boolean result. To see how to implement this function let's create $type
interpreter that checks object property type using typeof
operator:
import { createJsInterpreter } from '@ucast/js';
function type(condition, object, { get }) {
return typeof get(object, condition.field) === condition.value;
}
const interpret = createJsInterpreter({ type });
const condition = new FieldCondition('type', 'x', 'number');
interpret(condition, { x: 1 }); // true
Pay attention that object property is got by using get
function. Make sure that you always use get
function in custom operators to get object's property value, otherwise your operator will not support dot notation.
Want to help?
Want to file a bug, contribute some code, or improve documentation? Excellent! Read up on guidelines for contributing