How to convert decimal to integer in javascript

JS method of converting decimals to integers: 1. Use the "parseInt (decimal value)" statement; 2. Use the "~~decimal value" statement; 3. Use "Math.floor (decimal value)" statement; 4. Use the "Math.ceil (decimal value)" statement; 5. Use the "Math.round (decimal value)" statement.

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

Method 1: Use parseInt()

The parseInt() function parses a string and returns an integer.

When the value of parameter radix is ​​0, or the parameter is not set, parseInt() will determine the base of the number based on string.

When the parameter radix is ​​omitted, JavaScript defaults to the radix of numbers as follows:

• If the string starts with "0x", parseInt() will parse the rest of the string into ten Hexadecimal integer.

• If string starts with 0, then ECMAScript v3 allows an implementation of parseInt() to parse the following characters as octal or hexadecimal digits.

• If string starts with a number from 1 to 9, parseInt() will parse it into a decimal integer.

Example: Use parseInt() to parse different strings

document.write(parseInt("10") + "<br>");
document.write(parseInt("10.33") + "<br>");
document.write(parseInt("34 45 66") + "<br>");
document.write(parseInt(" 60 ") + "<br>");
document.write(parseInt("40 years") + "<br>");
document.write(parseInt("He was 40") + "<br>");
 
document.write("<br>");
document.write(parseInt("10",10)+ "<br>");
document.write(parseInt("010")+ "<br>");
document.write(parseInt("10",8)+ "<br>");
document.write(parseInt("0x10")+ "<br>");
document.write(parseInt("10",16)+ "<br>");

Output results:

10
10
34
60
40
NaN

10
10
8
16
16

Method 2: Negate twice

var decimal=4;
var integer = ~~decimal; // 4 = ~~4.123
console.log(integer);

Output result:

4

Method 3: Math.floor() round down

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

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

Method 4: Math.ceil() rounds up

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

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

Method 5: Math.round() rounding

Math.round(): Rounding.

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

[Recommended learning: javascript advanced tutorial]

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