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JavaScript Patterns 6.5 Inheritance by Copying Properties
Shallow copy pattern
function extend(parent, child) { var i; child = child || {}; for (i in parent) { if (parent.hasOwnProperty(i)) { child[i] = parent[i]; } } return child;}
Deep copy pattern
function extendDeep(parent, child) { var i, toStr = Object.prototype.toString, astr = "[object Array]"; child = child || {}; for (i in parent) { if (parent.hasOwnProperty(i)) { if (typeof parent[i] === "object") { child[i] = (toStr.call(parent[i]) === astr) ? [] : {}; extendDeep(parent[i], child[i]); } else { child[i] = parent[i]; } } } return child;}var dad = { counts: [1, 2, 3], reads: { paper: true }};var kid = extendDeep(dad);kid.counts.push(4);kid.counts.toString(); // "1,2,3,4"dad.counts.toString(); // "1,2,3"(dad.reads === kid.reads).toString(); // falsekid.reads.paper = false;kid.reads.web = true;dad.reads.paper; // true
Firebug (Firefox extensions are written in JavaScript) has a method called extend()that makes shallow copies and jQuery’s extend() creates a deep copy. YUI3 offers a method called Y.clone(), which creates a deep copy and also copies over functions by binding them to the child object.
Advantage
There are no prototypes involved in this pattern at all; it’s only about objects and their own properties.
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