How define function in javascript in global context inside a function?

Question

context = this
function test() {
  (function(cmd) {
    eval(cmd);
  }).call(context, 'function foo(){}');
};

test();
foo(); // => ReferenceError: foo is not defined

how can I define a global function inside a function ? (using nodeJS)

define a global function by adding it to ... global ... e.g global.yourFunctionName = function (arg1, arg2, ... , argN) { function body goes here }; — Jaromanda X
– Jaromanda X, Commented Sep 26, 2016 at 1:06
no because i use this function client side too, I can't add global.foo — Matrix
– Matrix, Commented Sep 26, 2016 at 1:15
I try to reduce the problem more simply ^^ but if necessary I can developed^^ — Matrix
– Matrix, Commented Sep 26, 2016 at 1:20

Community · Accepted Answer · 2017-05-23 10:27:24Z

1

A typical way to access the global object is calling a yielded value, e.g. from the comma operator.

function a() {
  (0, function () {
    this.foo = function () { console.log("works"); };
  })();
}
a();
foo();

UPDATE: Due to strict mode issues, here is another version (references: (1,eval)('this') vs eval('this') in JavaScript?, Cases where 'this' is the global Object in Javascript):

"use strict";
function a() {
  (0, eval)('this').foo = function () { console.log("works"); };
}
a();
foo();

edited May 23, 2017 at 10:27

CommunityBot

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answered Sep 26, 2016 at 1:13

ASDFGerte

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4 Comments

Matrix Over a year ago

What the hell... This works ! but I don't undersand why?

ASDFGerte Over a year ago

@Matrix see for example this question or this question

Matrix Over a year ago

your answer is amazing, it should be award you like 10 good answer! XD

ASDFGerte Over a year ago

@Matrix looking at the second question i referenced the comma seems even unnecessary here, a simple IIFE would be enough. However, the previously posted code would fail in strict mode on ES5. Therefore i added an update, which should also work on strict mode.

wilsonzlin · Accepted Answer · 2016-09-26 01:31:45Z

0

Use the global object in Node.JS:

function test() {
  eval('function foo() { return "this is global"; }');
  global.foo = foo;
};

test();

console.log(foo()); // this is global

edited Sep 26, 2016 at 1:31

answered Sep 26, 2016 at 1:15

wilsonzlin

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5 Comments

Matrix Over a year ago

I can't do this. Foo() is define in other file and be used server AND client side, it can't change, it define by function foo(), can't add "global"

wilsonzlin Over a year ago

@Matrix How is Foo defined in your other file? Is it global? Is it loaded alongside this script? Can you export the Foo function and require it in this script?

Matrix Over a year ago

in other file is just define global like function foo(){..}. I don't use require() because it need syntaxe module.export (this is incompatible with client side), so I read file and eval() it

wilsonzlin Over a year ago

@Matrix to make it compatible on the client side, just use if (typeof exports != "undefined") module.exports = Foo. It's recommended not to use eval as it's slow and sometimes dangerous (also the contexts get wacky, as you've found out)

wilsonzlin Over a year ago

@Matrix If you really want to use eval, and foo is declared in the global context in your other file: after evaling it in your function, just go global.foo = foo;, as I have reflected in the answer

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