35 lines
828 B
HTML
35 lines
828 B
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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<script>
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// var a=1
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// function test(){
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// alert(a) //undefined
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// var a=2
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// alert(a) //2
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// }
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// test()
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// alert(a) // 1
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// undefined 2 1
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// alert(Boolean("non-empty string")) //true
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// alert(Boolean(null)) //false
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alert(alert(1)||2||alert(3)) //1
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// alert(alert(1)&& alert(0)) //1
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// &&如果第一个是false就不走第二个。
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// alert没有返回值，所以布尔值是false
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// ||是第一个true不走第二个
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</script>
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</head>
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<body>
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</body>
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</html> |