How to convert value to int type in javascript

Javascript method to convert a value into an int type: 1. Use the "parseInt(value)" method to convert a value into an int integer; 2. Use "Math.floor(value)", "Math.ceil (value)" and "Math.round(value)" methods convert decimal values ​​into int integers.

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

Method 1: Use parseInt()

parseInt() is a global method that converts a value to an integer. 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

Method 2: Use Math.floor(), Math.ceil(), Math.round() to convert decimals to integers

There are 3 Math objects Static functions can be rounded

• Math.floor(): Returns the largest integer less than the parameter value.

• Math.ceil(): Returns the smallest integer greater than the parameter value.

• Math.round(): Rounding.

Example 1: The following code simply compares the values ​​​​of these three methods

console.log(Math.floor(2.5));  //2
console.log(Math.floor(-2.5));  //-3
console.log(Math.ceil(2.5));  //3
console.log(Math.ceil(-2.5));  //-2
console.log(Math.round(2.5));  //3
console.log(Math.round(-2.5));  //-2
console.log(Math.round(-2.6));  //-3

Example 2: The following code combines Math.floor() and Math.ceil( ) method, use JavaScript to design a function that rounds numbers

var toInt = function (num) {
    var num = Number(num);
    return num < 0 ? Math.ceil(num) : Math.floor(num);
}
console.log(toInt(2.5));  //2
console.log(toInt(-2.5));  //-2

[Recommended learning: javascript advanced tutorial]

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