Multiple ways of being judged as integers in JavaScript

Method one, using the remainder operator to judge

Any integer will be divisible by 1, that is, the remainder is 0. Use this rule to determine whether an integer.

function Isinteger (obj) {
return obj%1 = = 0
}
Isinteger (3)//True
Isinteger (3.3)//False

The above output can see that this function is very useful, but for strings and some special values appear powerless

Isinteger (')//True
Isinteger (' 3 ')//True
Isinteger (TRUE)//True
Isinteger ([])//True

It is difficult to accept the return of true for an empty string, a string type number, a Boolean true, or an empty array. Please refer to these types of internal conversion details: The false value of the wonderful flowers in JavaScript

Therefore, you need to first determine whether the object is a number, such as adding a typeof

function Isinteger (obj) {
return typeof obj = = ' number ' && obj%1 = 0
}
Isinteger (')//False
Isinteger (' 3 ')//False
Isinteger (True)//False
Isinteger ([])//False

Well, it's perfect.

Second, the use of Math.Round, Math.ceil, Math.floor judgment

Integers are equal to themselves after rounding. Use this feature to determine whether an integer, math.floor example, as follows

function Isinteger (obj) {
return Math.floor (obj) = = obj
}
Isinteger (3)//True
Isinteger (3.3)//False
Isinteger (')//False
Isinteger (' 3 ')//False
Isinteger (True)//False
Isinteger ([])//False

This directly masks the string, true,[], with less code than the previous function.

Third, through parseint judgment

function Isinteger (obj) {
return parseint (obj, ten) = = obj
}
Isinteger (3)//True
Isinteger (3.3)//False
Isinteger (')//False
Isinteger (' 3 ')//False
Isinteger (True)//False
Isinteger ([])//False

It's good, but there's one drawback.

Isinteger (1000000000000000000000)//False

Actually returned false, no justice. The reason is that parseint forces the first parameter to be parsed into a string before parsing the integer. This method of converting numbers to integers is not a good choice.

Four, through the position operation judgment

function Isinteger (obj) {
Return (obj 0) = = obj
}
Isinteger (3)//True
Isinteger (3.3)//False
Isinteger (')//False
Isinteger (' 3 ')//False
Isinteger (True)//False
Isinteger ([])//False

This function is very good, the efficiency is very high. But there is a flaw, mentioned above, the bitwise operation can only deal with the number of 32 digits, for more than 32-bit powerless, such as

1	isInteger(Math.pow(2, 32)) // 32位以上的数字返回false了

Of course, most of the time we don't use that big number.

V. ES6 provided the Number.isinteger

Number.isinteger (3)//True
Number.isinteger (3.1)//False
Number.isinteger (')//False
Number.isinteger (' 3 ')//False
Number.isinteger (True)//False
Number.isinteger ([])//False