Summary of JS implicit type conversion-JS Tutorial-php.cn

Summary of JS implicit type conversion

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Release： 2018-04-18 14:58:02

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This time I will bring you a summary of JS implicit type conversion . What are the precautions for JS implicit type conversion? The following is a practical case, let’s take a look.

Generally there are four situations, JavaScript will convert the data type of the variable.

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* if中的条件会被自动转为Boolean类型
 * 会被转为false的数据
 * 会被转为true的数据
* 参与+运算都会被隐式的转为字符串
 * 会被转为空字符串的数据
 * 会被转为字符串的数据
 * 会被转为数据类型标记的数据
* 参与*运算都会被隐式的转为数字
 * 会被转为0的数据
 * 会被转为1的数据
 * 会被转为NaN的数据
* == 运算符
 * 为true的时候
 * 为false的时候

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The conditions in if will be automatically converted to Boolean type

Data that will be converted to false

if(false) console.log(2333)
if('') console.log(2333)
if(null) console.log(2333)
if(undefined) console.log(2333)
if(NaN) console.log(2333)

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Data that will be converted to true

if(true) console.log(2333) // 2333
if('test') console.log(2333) // 2333
if([]) console.log(2333) // 2333
if({}) console.log(2333) // 2333

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All operations involved will be implicitly converted to string

Data that will be converted to an empty string

'str-' + '' // str-
'str-' + []

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Data that will be converted to string

'str-' + '1' // "str-1"
'str-' + 1 // "str-1"
'str-' + false // "str-false"
'str-' + true // "str-true"
'str-' + null // "str-null"
'str-' + undefined // "str-undefined"
'str-' + NaN // "str-NaN"

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Data that will be converted to data type tag

'str-' + {} // "str-[object Object]"
'str-' + {a:1} // "str-[object Object]"

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Participating in * operations will be implicitly converted to numbers

Data that will be converted to 0

2 * '' // 0
2 * [] // 0
2 * false // 0

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Data that will be converted to 1

2 * '1' // 2
2 * [1] // 2
2 * true // 2

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Data that will be converted to NaN

2 * {} // NaN
2 * {a:1} // NaN

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== operator

When it is true

0 == false // true
0 == '' // true
0 == '0' // true
0 == [] // true
0 == [0] // true
1 == true // true
1 == '1' // true
1 == [1] // true
[1] == true // true
[] == false // true

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When it is false

0 == {} // false
0 == null // false
0 == undefined // false
0 == NaN // false
1 == {} // false
1 == null // false
1 == undefined // false
1 == NaN // false
[] == [] // false
[1] == [1] // false
[1] == {} // false
[1] == {a:1} // false
[1] == false // false
[1] == null // false
[1] == undefined // false
[1] == NaN // false
{} == {} // false
{a:1} == {a:1} // false

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Note: The empty array [] is converted to the empty string '' under the operator, and is converted to the number 0 under the * operator. But in the if statement, it turns true.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!