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parseInt()

The effect is to cast an argument (usually a string) to an integer.

It has two parameters, the second one can be omitted, let's show you common usage first

1. Conversion rule: turn the number part of the string from left to right into an integer, once the conversion fails, NaN is returned.

(1)Parameter is string type:

var a = parseInt ('10 '); //Convert string to integer type

console.log(a); // 10

var b = parrseInt ('10 true'); //convert significant digits to integers, extract leading digits

console.log(b); // 10

var c = parseInt ('10 true 20'); //convert only the first significant part to an integer

console.log(c); //10

var d = parseInt ('045 zoo'); //The first part is converted to an integer, and the 0 before the number is omitted

console.log(d); //45

var f = parseInt ('34.5 '); //integer part, decimal point non-numeric part, truncated

console.log(f); //34

var g = parseInt ('a3 '); //If it does not start with a number, turn it into a special value of NaN (Not a Number is not a number)

console.log(g); //NaN

(2)Parameters are numeric types:

var a = parseInt(3.4); //still converted to numbers, but rounded

console.log(a); //3

(3)Other data types: as long as the beginning does not contain significant digits, the result will be NaN

var a = parseInt(true);

console.log(a); //NaN

var b = parseInt(null);

console.log(b); //NaN

var c = parseInt(undefined);

console.log(c); //NaN

var d = parseInt([]);

console.log(d); //NaN

var e = parseInt({});

console.log(e); //NaN

Next, let's look at the usage of the second parameter

The second parameter: indicates the base, range 2--36 (used to explain the base rule of the first parameter)

var a = parseInt ('99 ', 10); //This parameter can be omitted if the string is decimal

console.log(a); // 99

var a = parseInt ('1001 ',2); //' 1001 'conforms to binary rules, converts to decimal integers

console.log(a); // 9

var a = parseInt ('1001 ',10); //' 1001 'also conforms to decimal, converted to decimal integer

console.log(a); // 1001

var b = parseInt ('234 ', 2); //' 234 'does not conform to binary rules

console.log(b); // NaN

var b = parseInt ('abcde ',2); //' abcde 'does not conform to binary rules

console.log(b); // NaN

var c = parseInt ('1022 ', 2); //The' 10 'part is binary, but the' 22 'part is not, extract the first valid part and convert it to decimal

console.log(c); //2

Some special notes

If it starts with 0x or 0X, it can be recognized even if the base rule is not stated.

var e = parrseInt ('0xa '); //0x is hexadecimal representation, a is 10 in hexadecimal, automatically switched to decimal after conversion to integer

console.log(e); //10

Try not to use the number where e appears, because only the beginning part can be identified, which will cause confusion in the result.

The parseFloat method should be used instead

parseInt("6.022e23", 10); //returns 6

parseInt(6.022e2, 10); //returns 602

Very large or very small numbers

parseInt(4.7 * 1e22, 10); //very large values become 4

parseInt(0.000000000434, 10); //very small values become 4

In the latest ES5 specification, numbers that begin with 0 are no longer recognized as octal.

parseInt("011"); //will be converted from decimal to 11

parseInt("011", 8) //octal specified, result 9

The above is the content of this article about "how to use parseInt function". I believe everyone has a certain understanding. I hope the content shared by Xiaobian will be helpful to everyone. If you want to know more relevant knowledge content, please pay attention to the industry information channel.

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