CODEWITHSUNDEEP
javascriptjquerybackbone.jsrequirejsamd
hh54188
hh54188

Reputation: 15646

Why there is a 'amd' property in 'define' function?

I am learning jQuery and Backbone source code, and noticed they check if there is requirejs:

jQuery 1.9.1

if ( typeof define === "function" && define.amd && define.amd.jQuery ) {
    define( "jquery", [], function () { return jQuery; } );
}

Backbone

if (typeof define === 'function' && define.amd) {
    define(['underscore', 'jquery', 'exports'], function(_, $, exports) {

Why there always have a amd property in define function in requirejs?

And the define.amd always is an object which key jQuery is true? Even I have not import the jQuery module?

Upvotes: 2

Views: 698

Answers (1)

Louis
Louis

Reputation: 151441

It is a convention that AMD loaders should use to indicate that the define they export into the global space is the define that is made to be used by AMD modules to define themselves.

If AMD loaders did not use this convention then if some random JavaScript library decided to export a define function into the global space that has nothing to do with AMD, then code which is designed to work with or without an AMD loader would erroneously believe that they are used in an environment where an AMD loader is present.

There is still a risk for things to go askew if some random third party library decided to also export its own define function (that has nothing to do with defining AMD modules) and decided to add an amd property to it, but the risk is much lower than if the scheme I explained above was not used.

So jQuery and Backbone in the code you've shown tests whether it is used in an AMD environment where an AMD loader is present, and if so defines itself as an AMD module.

define.amd.jQuery is specific to jQuery and indicates that the loader is able to account for multiple version of jQuery being loaded simultaneously.

Upvotes: 2

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