@taqtile/ts-data-mapper
v0.7.1
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TypeScript data mapper
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Typescript Data Mapper
This module contains all default mapping operation and funcions commonly used by several projects.
Contents
Generic Mapper
Generic mapper is a type-safe function that receives the source object and an array of mappting operations
and apply these operations to create a mapped object. Differently from lodash's get, pick, omit
functions,
generic mapper checks in compilation time if the accessed properties are type safe (internally we still
use some of lodash's functions).
There are several built-in operations you can use and also a customizable option. Here is a full example of it's capabilities:
const source = { a: 1, b: false, c: undefined, d: '2' };
let target = map(source, ['a']); // { a: 1 }
const copy_b_to_be_op = {
from: 'b', to: 'be', invokeMethod: 'toString',
};
map(source, [copy_b_to_be_op], target); // { a: 1, be: 'false' }
const use_default_val_op = {
from: 'c', to: 'c', defaultValue: 'default',
};
map(source, [use_default_val_op]); // { c: 'default' }
const transform_op = {
from: 'd', to: 'd', transform: (value) => parseInt(value),
};
map(source, [transform_op]); // { d: 2 }
Copying property values
General case
The general and repeated common case is the mapping operation of renaming properties. For these kind of operations all you have to do is specify the source's property name and the target's property name.
const source: SourceType = { a: 1 };
const mapOps: MapOpArray<SourceType, MappedType> = [{ from: 'a', to: 'b' }];
const mapped: MappedType = map(source, mapOps); // { b: 1 }
Keeping the same property name
Another common case is to copy a property value into a property of the same name. You can use the
classical mapping operation { from: 'a', to: 'a' }
, but you can simply pass the property name:
const source: SourceType = { a: 1, b: 2, c: 3 };
const mapOps: MapOpArray<SourceType, MappedType> = ['a', 'b'];
const mapped: MappedType = map(source, mapOps); // { a: 1, b: 2 }
Default values
Sometimes you want to set a default value when there is none:
const source: SourceType = { a: 1, b: undefined };
const mapOps: MapOpArray<SourceType, MappedType> = ['a', { from: 'b', to: 'b', defaultValue: 2 }];
const mapped: MappedType = map(source, mapOps); // { a: 1, b: 2 }
!!! Warning !!!
- Default value will be used only if source's value is
undefined
.
Transforming mapped values
It's also possible to change the value retrieved from source by transforming it.
Invoking a value's method
If the transformation you want if a value's method, it's possible to safely use it by defining the invoke method name:
const source: SourceType = { a: 1, b: [2, 3], c: undefined };
const mapOps: MapOpArray<SourceType, MappedType> = [
{ from: 'a', to: 'a', invokeMethod: 'toString' },
{ from: 'b', to: 'b', invokeMethod: 'join', invokeArgs: ['-'] },
{ from: 'c', to: 'c', invokeMethod: 'toString' },
];
const mapped: MappedType = map(source, mapOps); // { a: '1', b: '2-3', c: undefined }
Custom transformation
It's also possible to use custom functions to alter a source's value:
const source: SourceType = { a: 1 };
const mapOps: MapOpArray<SourceType, MappedType> = [
{ from: 'a', to: 'a', transform: (value) => value + 1 },
];
const mapped: MappedType = map(source, mapOps); // { a: 2 }
!!! Warning !!!
- Transform invocation is not value safe, meaning that if value is
undefined
,transform
will be called withundefined
as argument
Existing target object
If you already have an object, you can pass it to be used as target:
const sourceA: SourceAType = { a: 1 };
const target: MappedType = map(sourceA, ['a']); // { a: 1 }
const sourceB: SourceBType = { b: 2 };
map(sourceB, ['b'], target); // mapped = { a: 1, b: 2 }
!!! Warning !!!
map
mutates the passed target objectmap
overrides existing properties values if there is an operation targeting the same property
Full MapOp cycle
The full map operation cycle is as follow:
- get value from source's property or get
defaultValue
- assign to value result from invoke method
- assign to value rsult from tranform function
- assign value to target's property