What does includes return in es6?

includes() in es6 returns a Boolean value. The includes() method is used to determine whether a string/array contains a specified value. The syntax is "ojb.includes(searchvalue, start)"; if a matching value is found, it returns true, otherwise it returns false.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

includes() method is used to determine whether the string/array contains the specified value; it will return a Boolean value indicating whether the string/array contains the given value.

Syntax:

ojb.includes(searchvalue, start)

Parameters	Description
searchvalue	Required, the string/array to be found.
start	Optional, set the position to start searching from, the default is 0.

Return value:

##Type DescriptionBoolean Returns true if a matching value is found, false otherwise.

Example: Find the string starting from the 12th index position

 var str = "Hello world, welcome to the Runoob.";
var n = str.includes("world", 12);
document.getElementById("demo").innerHTML = n;

Example 2: Check whether the array site contains phpcn

let site = ['phpcn', 'google', 'taobao']; 
site.includes('phpcn'); 
// true 
 site.includes('baidu'); 
// false

Compare the indexof method

The indexOf method has two shortcomings

First, it is not semantic enough , its meaning is to find the first occurrence position of the parameter value, so it is necessary to compare whether it is not equal to -1, which is not intuitive enough to express.

The second is that it uses the strict equivalent operator (===) internally for judgment, which will lead to misjudgment of NaN.

[NaN].indexOf(NaN)
 
// -1
 
includes使用的是不一样的判断算法，就没有这个问题。
 
[NaN].includes(NaN)
 
// true

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