https://github.com/pranaygp/proposal-array-prototype-do

tc39 array prototype do proposal
https://github.com/pranaygp/proposal-array-prototype-do

ecmascript tc39

Last synced: 11 days ago
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tc39 array prototype do proposal

• Host: GitHub
• URL: https://github.com/pranaygp/proposal-array-prototype-do
• Owner: pranaygp
• Created: 2017-10-05T00:28:55.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2017-10-05T04:15:59.000Z (over 7 years ago)
• Last Synced: 2025-01-20T16:53:39.641Z (13 days ago)
• Topics: ecmascript, tc39
• Size: 1.95 KB
• Stars: 0
• Watchers: 4
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Array.prototype.do proposal

This proposal introduces a new method to the Javascript Array prototype to support the common use case of performing side effects while iterating through an Array, while returning the original array paramenter. It is a pretty useful tool to help with the case where one finds themselves having to leave the chainability of function calls like `.map`, `.filter` and `.reduce`

## Inspiration

RxJS is an awesome library that almost lets you treat asynchronous events as elements in an array (called an Observable). RxJS has a [similarly named method on `Observable`](http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#instance-method-do) which is pretty useful.

## Introduction

The `Array.prototype.do` method is essentially synctactic sugar on a call to `Array.prototyp.map` that performs side effects before returning the first parameter of the callback.

For example:

```javascript

myArray.do(console.log)

```

is equivalent to 

```javascript

myArray.map(x => {

  console.log(x);

  return x;

})

```

## Proposed API 

```javascript

arr.do(function callback(currentValue, index, array) {

    // Return element for new_array

}[, thisArg])

```

### Parameters

`callback`

  Function that performs the intended side effect, taking three arguments:

  `currentValue`

    The current element being processed in the array.

  `index`

    The index of the current element being processed in the array.

  `array`

    The array `do` was called upon.

  

`thisArg`

  Optional. Value to use as `this` when executing callback.

### Return value

The original array that `.do` was called on

### Examples

Debugging (example inspired from [RxJS docs](http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#instance-method-do)

```javascript

let clicks = ... // events

let positions = clicks

  .do(console.log)  // easy to add line when debugging

  .map(ev => ev.clientX)

```

Filtering function applications

```javascript

let allFiles = ... // list of files

allFiles

  .do(someFunctionForAllFiles)

  .filter(s => s.endsWith('.js'))

  .do(someFunctionForJSFilesOnly)

```