不理解，如果有高手看到了，请帮忙解答，谢谢啦~

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不理解，如果有高手看到了，请帮忙解答，谢谢啦~

例1：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
//a.constructor.toString().indexOf("Array") > -1+" "+
//typeof a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例1结果：
constructor 属性返回变量或对象的构造函数。

function String() { [native code] }
function Number() { [native code] }
function Boolean() { [native code] }
function String() { [native code] }
function Array() { [native code] }
function
function Array() { [native code] }
string
9
number
function Object() { [native code] }
function Date() { [native code] }
function Function() { [native code] }

例2：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
a.constructor.toString().indexOf("Array") > -1+" "+
//typeof a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例2 结果：
constructor 属性返回变量或对象的构造函数。

true

例3：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
a.constructor.toString().indexOf("Array") > -1+" "+
typeof a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例3结果：
constructor 属性返回变量或对象的构造函数。

false

例4：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
//a.constructor.toString().indexOf("Array") > -1+" "+
typeof a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例4结果：
constructor 属性返回变量或对象的构造函数。

true

例5：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor+" "+
typeof a.constructor.toString().indexOf("Array") > -1;
</script>

</body>
</html>

例5结果：
constructor 属性返回变量或对象的构造函数。

true

例6：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
typeof a.constructor.toString().indexOf("Array") > -1+" "+;
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例6结果：
constructor 属性返回变量或对象的构造函数。

例7：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
typeof a.constructor.toString().indexOf("Array") > -1+" "+
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例7结果：
constructor 属性返回变量或对象的构造函数。

false

例8：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>

 constructor 属性返回变量或对象的构造函数。

<script>
var a=[1,2,3,4];
document.getElementById("demo").innerHTML =
typeof a.constructor.toString().indexOf("Array") > -1+" "+
"john".constructor + " " +
(3.14).constructor + " " +
false.constructor + " " +
"b".constructor+" "+
a.constructor + " " +
typeof a.constructor + " " +
a.constructor.toString()+" "+
typeof a.constructor.toString()+" "+
a.constructor.toString().indexOf("Array")+" "+
typeof a.constructor.toString().indexOf("Array")+" "+
//a.constructor.toString().indexOf("Array") > -1+" "+
{name:'john', age:34}.constructor + " " +
new Date().constructor + " " +
function () {}.constructor;
</script>

</body>
</html>

例8结果：
constructor 属性返回变量或对象的构造函数。

true

问题：(typeof a.constructor.toString().indexOf("Array")) > -1 的摆放位置决定了最后的结果，该句只有放在最后的时候，输出才是true，其它位置都是false，为什么？

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原文地址：https://www.cnblogs.com/cyy-13/p/5760260.html