Detailed explanation of conversion between JS numbers and strings

This article mainly brings you a brief explanation of examples of conversion between JS numbers and strings. The editor thinks it’s pretty good, so I’ll share it with you now and give it as a reference. Let’s follow the editor to take a look, I hope it can help everyone.

Convert string to number

1 parseInt() function

parseInt() function parses from the beginning of string and returns an integer
parseInt('123'): Returns 123;
parseInt('1234xxx'): returns 1234;
parseInt('123.456'): returns 123;
parseInt('1 2 3'): returns 1; in the case of string, since Will return the first number
parseInt('bb cc 12'): Return NaN; if the first string is not a number, return nan
parseInt('123' 321): Return 321;
parseInt( "AF", 16); returns 175; it will automatically convert binary hexadecimal to octal into numbers

If the number cannot be parsed, a NaN value will be returned. You can use the isNaN() function to Detection;

parseFloat() will only return decimals

2 characters preceded by "+"

var n =+"123": return 123

3 characters plus "*"

var n ="123"*1: return 123

4 Add string array splitting

var arr = str.split(", ") A string group is divided into multiple by using
b = a.join("-");- is the specified separator, you can convert the array into a string at will

5 Adding a string and a number returns a string

console.log(12+"12"):返回"1212" console.log('12' + '34')返回'1234' console.log('12' + 34 ) 返回'1234' console.log(12 + '34''）返回1234' console.log(12 + 34 ) 返回46

6 When adding a string and multiple numbers, expand them with brackets

("") 返回("")

If you want to convert it to 3

("") 返回("")

If it is preceded by the addition of numbers, you can add the numbers first

var a = 10 + 20 + 'abc' + 'cd'; 返回a的值为:30abccd

7eval()If you want to perform string operations

eval("x=10;y=20;document.write(x*y)") 返回200 document.write(eval("2+2"))　　　　　　返回4 var x=10 document.write(eval(x+17）　　　　　　返回27

Convert numbers to strings

1 tostring（） n = 100x = n.toString() => "100"或是（100）toString() //tostring（2/16/8）还可以实现进制的转化

2 Number + any string ""

var n = 1234;var nn = 1234+"" -------------------------------------------------

About the string

Determine whether the string contains and returns the subscript. If it does not contain, return -1

　var i = str.indexOf("x")

The string of the last subscripted string

　var i = str .lastIndexOf("")

Convert to uppercase and lowercase

str.toUpperCase() 转大写 　　str.tolowerCase() 转小写

Intercept string string.substr ("Start from", "Intercept a few" )

　str.substr(0,5) 

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