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, Sep 26 '16 at 01:06
no because i use this function client side too, I can't add global.foo — Matrix, Sep 26 '16 at 01:15
I try to reduce the problem more simply ^^ but if necessary I can developed^^ — Matrix, Sep 26 '16 at 01:20

score 1 · Accepted Answer · edited May 23 '17 at 10:27

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 '17 at 10:27

Community

1
1

answered Sep 26 '16 at 01:13

ASDFGerte

4,695
6
16
33

What the hell... This works ! but I don't undersand why? – Matrix Sep 26 '16 at 01:36
@Matrix see for example [this question](http://stackoverflow.com/questions/4295175/cases-where-this-is-the-global-object-in-javascript) or [this question](http://stackoverflow.com/questions/9107240/1-evalthis-vs-evalthis-in-javascript/9107304) – ASDFGerte Sep 26 '16 at 01:40
your answer is amazing, it should be award you like 10 good answer! XD – Matrix Sep 26 '16 at 01:51
1

@Matrix looking at the [second question i referenced](http://stackoverflow.com/questions/4295175/cases-where-this-is-the-global-object-in-javascript) 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`. – ASDFGerte Sep 26 '16 at 02:16

wilsonzlin · Answer 2 · 2016-09-26T01:31:45.650

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 '16 at 01:31

answered Sep 26 '16 at 01:15

wilsonzlin

2,154
1
12
22

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" – Matrix Sep 26 '16 at 01:19
@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? – wilsonzlin Sep 26 '16 at 01:22
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 – Matrix Sep 26 '16 at 01:25
@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 Sep 26 '16 at 01:26
@Matrix If you really want to use eval, and `foo` is declared in the global context in your other file: after `eval`ing it in your function, just go `global.foo = foo;`, as I have reflected in the answer – wilsonzlin Sep 26 '16 at 01:31

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

2 Answers2