Avoid use of
== and != JS-0050
Anti-pattern
Minor
a year ago
—
a year old
Expected '===' and instead saw '=='
3
4 let p,i;
5 for (p = 2; p * p < MAX_SIZE;p++) {
6 if (IsPrime[p] == true) { 7 for(i = p * p; i < MAX_SIZE; i += p)
8 IsPrime[i] = false;
9 }Expected '!==' and instead saw '!='
1function gcd(a, b) {
2 while (b != 0) { 3 c = a % b;
4 a = b;
5 b = c;Expected '===' and instead saw '=='
1function smallestFactor(x) {
2 for (i = 2; i <= Math.floor(x**.5); i++) {
3 if (x % i == 0) { 4 return i;
5 };
6 };
Description
It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.
The strict equality operators (=== and !==) use the strict equality comparison algorithm to compare two operands.
- If the operands are of different types, return
false. - If both operands are objects, return
trueonly if they refer to the same object. - If both operands are
nullor both operands areundefined, returntrue. - If either operand is
NaN, returnfalse. - Otherwise, compare the two operand's values:
- Numbers must have the same numeric values.
+0and-0are considered to be the same value. - Strings must have the same characters in the same order.
- Booleans must be both
trueor bothfalse.
- Numbers must have the same numeric values.
The most notable difference between this operator and the equality (==) operator is that if the operands are of different types, the == operator attempts to convert them to the same type before comparing.
Bad Practice
a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
Recommended
a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null