js in operator

in operator: (?in?) The first parameter is a string or other types that can be converted, the 2 parameter is an operation object or an array, and the value of the first operand is the attribute name of the second operand.

example

<!-- <script type="text/javascript">

function FF() {

this.age = 11;

}

FF.prototype.name = "kevin";

// in is used to determine whether the attribute exists in the object

var flag1 = "age" in new FF()? "Existing": "Not Existing";

var flag2 = "name" in new FF()? "Exist": "Not Exist";

alert(flag1)

alert(flag2)

</script> -->

<script type="text/javascript">

var key=new Array('java','javascrit','html')

var str = 'java';

if( 1 in key){

alert('This exists in this array')

}else(

alert('not inside')

)

</script>

Instructions:

1. Judgment

x in arr Here we should pay attention to the fact that when judging the array, x means the subscript. This consciousness is that there is an element with the subscript x in the arr array

x in obj The current x represents the attribute of the object, which means whether there is an attribute of x in obj

Sample code:

 

1. var arr = [1,4,6,'a'];

2. console.log('a' in arr);

3. console.log(4 in arr);

4. console.log(3 in arr);

The result of this output is: false false true;

 

Explanation: The first false, because the subscript cannot be a; the second false, because the length of the arr array is 4, the subscript is 0, 1, 2, 3 without subscript 4; the third is true, the reason Same as the second one

 

Sample code:

 

1. var obj = {a:3,b:'b',c:'4'}

2. console.log('a' in obj)

3. console.log('b' in obj)

4. console.log('4' in obj)

The output result is: true, true, false

 

Explanation: The first one is true because there is attribute a in obj; the second one is true because there is attribute b in obj, not because the value is b, which is why the third one is false

 

2. ...in... traverse arrays or objects

Traverse the array code:

 

1. var arr = [1,2,3,4,5,6,7]

2. for(var x in arr){

3. console.log(arr[x])

4. }

The output result is: 1 2 3 4 5 6 7

 

 

Traverse the object code:

 

1. var obj = {a:1,b:'c',d:3}

2. for(var x in obj){

3. console.log(obj[x])

4. }

The output result is: 1 c 3