How to convert value to numeric type in javascript

Method for converting to numeric type: 1. Use the parseInt() function to convert the value to an integer, the syntax is "parseInt(value)"; 2. Use the parseFloat() function to convert the value to a float Points, the syntax is "parseFloat(value)"; 3. Use the multiplication operator, the syntax is "value*1".

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

javascript method to convert value to numeric type:

Method 1: Use parseInt() function

parseInt() is a global method that converts values ​​to integers. The conversion process is as follows:

• First parse the character at position 0. If it is not a valid number, NaN will be returned directly.

• If the character at position 0 is a number or can be converted to a valid number, continue to parse the character at position 1. If it is not a valid number, return the valid character at position 0 directly. number.

• And so on, analyzing each character one by one from left to right until a non-numeric character is found.

• parseInt() will convert all previously analyzed legal numeric characters into numerical values ​​and return them.

console.log(parseInt("123abc"));  //返回数字123
console.log(parseInt("1.73"));   //返回数字1
console.log(parseInt(".123"));   //返回值NaN

Dots in floating-point numbers are illegal characters for parseInt(), so the decimal part of the value will not be converted.

If it is a numeric string starting with 0, parseInt() will treat it as an octal number: first convert it to an octal value, and then convert it to a decimal number and return it.

If it is a numeric string starting with 0x, parseInt() will treat it as a hexadecimal number: first convert it to a hexadecimal value, and then convert it to a decimal number and return .

var d = 010;  //八进制数字字符串
var e = 0x10;  //十六进制数字字符串
console.log(parseInt(d));  //返回十进制数字8
console.log(parseInt(e));  //返回十进制数字16

parseInt() also supports base mode, which can convert digital strings in different bases such as binary, octal, and hexadecimal into integers. The base mode is specified by the second parameter of the parseInt() function.

Example

The following code converts binary, octal and decimal digit strings into decimal integers.

console.log(parseInt("10",2));  //把二进制数字 10 转换为十进制整数，为 2
console.log(parseInt("10",8));  //把八进制数字 10 转换为十进制整数，为 8
console.log(parseInt("10",10));  //把十进制数字 10 转换为十进制整数，为 10

Method 2: Use parseFloat() function

parseFloat() is also a global method, which can convert the value to a floating point number, that is, it can identify the first occurrences of a decimal point, and the second decimal point is considered illegal. The parsing process is the same as the parseInt() method.

console.log(parseFloat("1.234.5"));  //返回数值 1.234

The parameter of parseFloat() must be a string in decimal form, and octal or hexadecimal numeric strings cannot be used. At the same time, 0 (octal number identification) in front of the number will be ignored, and 0 will be returned for hexadecimal numbers.

console.log(parseFloat("123"));  //返回数值 123
console.log(parseFloat("123abc"));  //返回数值 123
console.log(parseFloat("010"));  //返回数值 10
console.log(parseFloat("0x10"));  //返回数值 0
console.log(parseFloat("x10"));  //返回数值 NaN

Method 3: Use the multiplication operator

If the variable is multiplied by 1, the variable will be automatically converted to a numeric value by JavaScript. After multiplying by 1, the result is unchanged, but the type of the value is converted to a numeric value. If the value cannot be reduced to a legal number, NaN is returned.

var a = 1;  //数值
var b = "1";  //数字字符串
console.log(a + (b * 1));  //返回数值 2

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