内置对象Global,Math

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var box = '//dog学';
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var a = encodeURI(box);
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var b = encodeURIcomponent(box);     //%2F%2Fdog%E5%AD%A6
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alert(a);    // //dog%E5%AD%A6
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alert(b);    // %2F%2Fdog%E5%AD%A6
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alert(decodeURI(a));     // //dog学
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alert(decodeURIComponent(b));     //     //dog学

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eval('var box = 100');
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alert(box);
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eval(alert(100));     //100
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alert(eval(alert(100)));     //100,undefined  第一个打印100,第二个打印eval的返回值
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eval('function box(){return 123}');
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alert(box());     //123

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alert(Math.E);     //2.718281828459045
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alert(math.PI);     //3.141592653589793
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alert(Math.min(2,5,8,0));     //0
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alert(Math.max(2,5,8,0));     //8
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alert(Math.abs(-5));     //5
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alert(Math.sqrt(9));     //3
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alert(Math.ceil(25.1));     //26
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alert(Math.ceil(25.5));     //26
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alert(Math.ceil(25.9));     //26,向上舍入
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alert(Math.floor(25.1));     //25
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alert(Math.floor(25.5));     //25
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alert(Math.floor(25.9));     //25,向下舍入
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3 collapsed lines
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alert(Math.round(25.1));     //25
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alert(Math.round(25.5));     //26
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alert(Math.round(25.9));     //26,标准的四舍五入

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for (var i = 0; i < 10; i++) {
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  document.write(Math.floor(Math.random() * 10 + 1));
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  document.write('<br />');
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}     //1-10之间
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for (var i = 0; i < 10; i++) {
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  document.write(Math.floor(Math.random() * 6 + 5));
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  document.write('<br />');
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}     //5-10之间
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function select(start, end) {
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  var total = end - start + 1;
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  return Math.floor(Math.random() * total + start);
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}
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4 collapsed lines
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for (var i = 0; i < 10; i++) {
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  document.write(select(5, 10));
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  document.write('<br />');
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}     //5-10之间