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POTrying to understand underscore.js source - call and apply used in library
 

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    <p>In Jeremy Ashkenas's awesome Underscore.js library, I tried to understand one thing about the source file. I do not understand this:</p> <pre><code>var slice = Array.prototype.slice; args = slice.call(arguments, 2); </code></pre> <p>So that:</p> <pre><code>args = Array.prototype.slice.call(arguments, 2); </code></pre> <p><code>.call</code> or <code>.apply</code> are the methods of the functions. But here, which functions do <code>.call</code> refer to? The first parameter should be the context, but <code>arguments</code> is context? The second parameter should be the params to pass in the functions. Here they are number <code>2</code>. What does this mean? Sometimes in the library, it uses <code>1</code> or <code>0</code>. Are they the number of the params to pass in the functions?</p> <pre><code>_.bind = function bind(func, context) { var bound, args; if (func.bind === nativeBind &amp;&amp; nativeBind) return nativeBind.apply(func, slice.call(arguments, 1)); if (!_.isFunction(func)) throw new TypeError; args = slice.call(arguments, 2); return bound = function() { if (!(this instanceof bound)) return func.apply(context, args.concat(slice.call(arguments))); ctor.prototype = func.prototype; var self = new ctor; var result = func.apply(self, args.concat(slice.call(arguments))); if (Object(result) === result) return result; return self; }; }; </code></pre> <p>Question 2: I do not quite understand the logic of this function. Need help to understand. An example should be very helpful.</p> <pre><code> // Invoke a method (with arguments) on every item in a collection. _.invoke = function(obj, method) { var args = slice.call(arguments, 2); return _.map(obj, function(value) { return (method.call ? method || value : value[method]).apply(value, args); }); }; </code></pre> <p>Thank you for help.</p>
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