【众秒之门 JavaScript与jQuery技术精粹 #BOOK#】第4章 数据类型及定义

时间：2023-11-22 20:27:44
<!DOCTYPE html>

<html lang="zh-CN">

<head>

    <meta charset="utf-8">

    <title></title>

</head>

<body>

    <script>

        // NULL表示没有值，那么很明显它不能作为任何东西的实例

        console.log(typeof null) // object

        console.log(null instanceof Object) // false

        // NaN 即not a numbaer

        console.log(typeof NaN) // number

        console.log(NaN === NaN) // false

        // 空数组实际上等于true，但是在和布尔值比较时，却被看作false

        var someVar = []

        console.log(someVar == false)

        if (someVar) {

            console.log('hello')

        }

        // 正则表达式

        console.log('10 13 21 48 52'.replace(/\d+/g, '*'))

        console.log('10 13 21 48 52'.replace(/\d+/g, function(match) {

            return parseInt(match, 10) < 30 ? '*' : match

        }))

        console.log(/\w{3,}/.test('Hello'))

        function findWord(word, string) {

            var instancesOfWord = string.match(new RegExp('\\b' + word + '\\b', 'ig'))

            console.log(instancesOfWord)

        }

        findWord('car', 'Carl went to buy a car but had forgotten his credit card.')

        var animal = 'dog'

        function getAnimal(adjective) {

            console.log(adjective + ' ' + this.animal)

        }

        var myObj = {

            animal: 'camel'

        }

        getAnimal.call(myObj, 'lovely')

        var someVar = 'hello'

        setTimeout((function(someVar) {

            return function() {

                console.log(someVar)

            }

        })(someVar), 1000)

        someVar = 'goodbye'

        console.log(0.1 + 0.2)

    </script>

</body>

</html>

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