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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
Whenusing 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])
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)
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)
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)
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)
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)
url: The network resource address that needs to be decoded.
Description: This function can convert the network resource address transcoded usingencodeURI() 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>
4. Running results
(1) Use the parseInt() function:123abc The conversion result is: 123
(2) Use the parseFloat() function:
abc123 The conversion result is: NaN123.456789abc The conversion result is: 123.456789
(3) Use the isNaN() function:123.456789abc Whether it is NaN after conversion: false
(4) Use the isFinite() function
abc123 Whether it is NaN after conversion: trueto determine whether the result of dividing 1 by 0 is infinity: false
(5) Use the encodeURI() functionto convert the network resource address to: http:// 127.0.0.1/save.html?name=Test
(6) Use the decodeURI() functionto 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!
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