Detailed explanation of conversion between JS numbers and strings-JS Tutorial-php.cn

Detailed explanation of conversion between JS numbers and strings

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Release： 2018-05-31 09:06:17

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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(&#39;12&#39; + &#39;34&#39;)返回&#39;1234&#39; 
console.log(&#39;12&#39; + 34 ) 返回&#39;1234&#39; 
console.log(12 + &#39;34&#39;&#39;）返回1234&#39; 
console.log(12 + 34 ) 返回46

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

("<img src=&#39;images/" + 2 + 1 + ".jpg&#39;>") 返回("<img src=&#39;images/" + 21 + ".jpg&#39;>")

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If you want to convert it to 3

("<img src=&#39;images/" + （2+1）+ ".jpg&#39;>") 返回("<img src=&#39;images/" + 3 + ".jpg&#39;>")

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

var a = 10 + 20 + &#39;abc&#39; + &#39;cd&#39;; 返回a的值为:30abccd

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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

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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

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2 Number + any string ""

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

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About the string

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

　var i = str.indexOf("x")

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The string of the last subscripted string

　var i = str .lastIndexOf("")

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Convert to uppercase and lowercase

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

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

　str.substr(0,5)
<body>

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