Summary of commonly used built-in functions in JS-JS Tutorial-php.cn

Summary of commonly used built-in functions in JS

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Release： 2018-05-21 14:56:58

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This time I will bring you a summary of commonly used built-in functions in JS. What are the precautions for using commonly used built-in functions in JS? The following is a practical case, let’s take a look.

1. Introduction

When

using JavaScript language, in addition to custom functions In addition, you can also use JavaScript's built-in functions, which are functions provided by the JavaScript language itself.

2. A detailed introduction to some commonly used built-in functions

1. parseInt() function

This function mainly converts a string whose first digit is a number into a number. If the string does not start with a number, NaN will be returned.

Syntax:

parseInt(StringNum,[n])

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StringNum: A string that needs to be converted to an integer.
n: Provide a number between 2 and 36 to represent the base number of the saved number. This parameter is not required in the function.

2. parseFloat() function

This function mainly converts a string whose first digit is a number into a floating-point number. If the string does not start with a number, then will return NaN.

Syntax:

parseFloat(StringNum)

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StringNum: A string that needs to be converted to a floating point type.

3. isNaN() function

This function is mainly used to check whether a value is NaN.

Syntax:

isNaN(Num)

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Num: The number that needs to be verified.

Note: If the parameter Num is NaN, the function returns a value of true; if the parameter Num is not NaN, the function returns a value of false.

4. isFinite() function

This function is mainly used to check whether an expression is infinite.

Syntax:

isFinite(Num)

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Num: The number that needs to be verified.

Description: If the parameter Num is infinity, the function returns a value of true; if the parameter Num is not infinite, the function returns a value of false.

5. encodeURI() function

This function is mainly used to return the encoded result of a URI string.

Syntax:

encodeURI(url)

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url: A string that needs to be converted into a network resource address.

Note: Both URI and URL can represent network resource addresses. URI has a wider representation range than URL, but in general, URI and URL can be equivalent.

encodeURI()The function only escapes meaningful characters in the string. For example, convert spaces in the string to " ".

6. decodeURI() function

This function is mainly used to decode the string encoded as URI into the original string and return it.

Syntax:

decodeURI(url)

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url: The network resource address that needs to be decoded.

Description: This function can convert the network resource address transcoded using

encodeURI() into a string and return it, that is, the decodeURI() function is The reverse operation of encodeURI() function.

3. Code

<script type="text/javascript">
/*
parseInt()函数
*/
var num1="123abc"
var num2="abc123"
document.write("（1）使用parseInt()函数:<br>");
document.write("123abc转化结果为:"+parseInt(num1)+"<br>");
document.write("abc123转化结果为:"+parseInt(num2)+"<br><br>");
/*
parseFloat()函数
*/
var num3="123.456789abc"
document.write("（2）使用parseFloat()函数：<br>");
document.write("123.456789abc转化结果为:"+parseFloat(num3)+"<br><br>");
/*
isNaN()函数
*/
document.write("（3）使用isNaN()函数：<br>");
document.write("123.456789abc转化后是否为NaN:"+isNaN(parseFloat(num3))+"<br>");
document.write("abc123转化结果后是否为NaN:"+isNaN(parseInt(num2))+"<br><br>");
/*
isFinite()函数
*/
document.write("（4）使用isFinite()函数<br>");
document.write("1除以0的结果是否为无穷大："+isFinite(1/0)+"<br><br>");
/*
encodeURI()函数
*/
document.write("（5）使用encodeURI()函数<br>");
document.write("转化为网络资源地址为："+encodeURI("http://127.0.0.1/save.html?name=测试")+"<br><br>");
/*
decodeURI()函数
*/
document.write("（6）使用decodeURI()函数<br>");
document.write("转化网络资源地址的字符串为："+decodeURI(encodeURI("http://127.0.0.1/save.html?name=测试"))+ "<br><br>");
</script>

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4. Running results

(1) Use the parseInt() function:
123abc The conversion result is: 123
abc123 The conversion result is: NaN
(2) Use the parseFloat() function:
123.456789abc The conversion result is: 123.456789
(3) Use the isNaN() function:
123.456789abc Whether it is NaN after conversion: false
abc123 Whether it is NaN after conversion: true
(4) Use the isFinite() function
to determine whether the result of dividing 1 by 0 is infinity: false
(5) Use the encodeURI() function
to convert the network resource address to: http:// 127.0.0.1/save.html?name=Test
(6) Use the decodeURI() function
to convert the string of the network resource address to: http://127.0.0.1/save.html?name =Test

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!