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getSingle.html
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getSingle.html
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<!DOCTYPE HTML>
<html lang="zh-CN">
<head>
<title>单例模式的例子</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1,user-scalable=no" />
</head>
<body>
<p>下面是一个单例模式的例子，在第三部分设计模
式的学习中，我们将进行更深入的讲解，这里暂
且只了解其代码实现：</p>
<pre>
var getSingle = function ( fn ) {
var ret;
return function () {
return ret || ( ret = fn.apply( this,
arguments ) );
};
};
</pre>
<p>这个高阶函数的例子，既把函数当作参数传递，
又让函数执行后返回了另外一个函数。我们可以
看看getSingle函数的效果：</p>
<pre>
var getScript = getSingle(function(){
return document.createElement( 'script' );
});
var script1 = getScript();
var script2 = getScript();
alert ( script1 === script2 ); // 输出：true
</pre>
<script>
var getSingle = function (fn) {
var ret;
return function () {
return ret || (ret = fn.apply(this,arguments));
};
};
var getScript = getSingle(function () {
return document.createElement('script');
});
var script1 = getScript();
var script2 = getScript();
console.log(script1 === script2); // 输出：true
//////////////////////////////////
var getScript2 = function () {
return document.createElement('script');
};
var script11 = getScript2();
var script22 = getScript2();
console.log(script11 === script22); // 输出：false
</script>
</body>
</html>