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<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>参数默认值</title>
</head>
<body>
<script>
function multiply(a, b) {
a = a || 5; //注意如果是undefined的话默认会选择5
b = b || 3; //注意如果是undefined的话默认会选择3
return a * b;
}
console.log(multiply()); //15
console.log(multiply(1, 2)); //2
/*
对于ES6来说,操作就简单多了。
*/
function multiply1(a = 5, b = 3) {
return a * b;
}
console.log(multiply1()); //15
console.log(multiply1(1, 2)); //2
/*
注意如果a你准备不传值,使用默认值的时候,就输入undefined;
如果a你准备输入的是:null,默认给你个0;
*/
console.log(`a输入undefined,最后结果为:${multiply1(undefined, 2)}`); //10
console.log(`a输入null,最后结果为:${multiply1(null, 2)}`); //0
//console.log(multiply1( ,2)); //报错:Uncaught SyntaxError: Unexpected token ,
</script>
</body>
</html>
函数的扩展:函数参数的默认值
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转载自blog.csdn.net/JEFF_luyiduan/article/details/91459816
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