javascript - Extending Array.prototype in Node.js, from a require'd file - Stack Overflow

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I have the following saved in test.js. It successfully extends Array in the browser, but it doesn't seem to work with node and require. Can someone explain what's wrong here?

(function() {

Array.prototype.max = function() {
  return console.log("Array.prototype.max");
};
return Array.max = function() {
  return console.log("Array.max");
};

}).call(this);

Then, from a terminal:

> My-MacBook-Pro: me$ node
> var test = require("./test")
> [1,2,3].max()
TypeError: Object 1,2,3 has no method 'max'
    at [object Context]:1:9
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)
> Array.max()
TypeError: Object function Array() { [native code] } has no method 'max'
    at [object Context]:1:7
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)

I have the following saved in test.js. It successfully extends Array in the browser, but it doesn't seem to work with node and require. Can someone explain what's wrong here?

(function() {

Array.prototype.max = function() {
  return console.log("Array.prototype.max");
};
return Array.max = function() {
  return console.log("Array.max");
};

}).call(this);

Then, from a terminal:

> My-MacBook-Pro: me$ node
> var test = require("./test")
> [1,2,3].max()
TypeError: Object 1,2,3 has no method 'max'
    at [object Context]:1:9
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)
> Array.max()
TypeError: Object function Array() { [native code] } has no method 'max'
    at [object Context]:1:7
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)

• javascript
• node.js
• require

Share Improve this question Follow asked Apr 21, 2011 at 4:59 GeoffGeoff 9,5901313 gold badges5454 silver badges6969 bronze badges 3

• Have you tried it outside of the REPL (i.e. running it in a file)? – Cristian Sanchez Commented Apr 21, 2011 at 5:22
• think I found it, see my updated answer. – KooiInc Commented Jun 5, 2011 at 11:39
• This example now works in Node 0.6. It is confirmed not to work in 0.4.1. – Tristan Commented Nov 8, 2011 at 10:04

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2 Answers 2

Sorted by: Reset to default 10

You can create a file which includes your extensions:

array.extensions.js

if(!Array.prototype.Last){
    Array.prototype.Last = function(){
        return this.slice(-1)[0];
    }
}

if(!Array.prototype.First){
    Array.prototype.First = function(){
        return this[0];
    }
}

then include this file to your startup file.

app.js:

require('{path}/array.extensions');
var express = require('express');
/* rest of your code */

referring this file once on startup is enough to use...

Every mand in the REPL is executed via vm.runInContext with a shared context object. This object is created at REPL initialization by copying everything from the global object. Since the require'd module will only extend Array.prototype after it has been copied to the context object, the modified version is never exposed.

Or at least that's what I could deduce from the source code. I know nothing about the inner workings of V8 :) And as you probably have found out by now, your example works fine outside the REPL.

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