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Editorial Team
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Asked: 2026-06-05T09:23:19+00:00

I realize I could answer myself with a simple test project (and I may,

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I realize I could answer myself with a simple test project (and I may, if no-one chimes in right away), but I couldn’t find the answer anywhere on SO or google, and it seems critical:

If I define an AMD module with require.js as such: 

//a.js
define( ['stuff'], function (Stuff) {
     return { thing: new Stuff() };
}

And then I use it in two different other modules as such:

// b.js
define( ['a'], function(a) {
    // do something with a's stuff 
});

// c.js
define( ['a'], function(a) {
  //do something else with a's stuff
}

Does a‘s defining function get called (and therefore a new Stuff instantiated) each time I require it for another module or does it just get called once, and its output gets cached?

Obviously this is critical in some use-cases, but its not clear from the require.js documentation or other examples I’ve seen.

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1 Answer

  1. Editorial Team

    I just tested this out myself, and it looks like the constructor is only run once.

    // stuff.js
define(function() {
    return function() {
        console.log('making new!');
    };
});

// a.js
define( ['stuff'], function (Stuff) {
     return { thing: new Stuff };
});

// b.js
define( ['a'], function(a) {
});

// c.js
define( ['a'], function(a) {
});

// app.js
define(['b', 'c'], function() {
    console.log('app');
});

// index.html
<html>
<head>
    <script src='requirejs/require.js' data-main='app.js'></script>
</head>
</html>

    When I open index.html, the console shows:

    making new!                             stuff.js:3
app                                       app.js:2
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