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JavaScriptBeginner#coercion
JavaScriptBeginner#operators#coercion
Explain == vs ===.
=== compares type and value with no conversion. == performs type coercion first, which produces surprising results, so prefer === everywhere except the idiomatic x == null check.
Example
0 == '0'; // true 0 === '0'; // false null == undefined; // true null === undefined; // false