| 2. 9. 1. Equal and Not Equal |
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if (x % 2 != 0)
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document.write(x);
}
// -->
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The equal operator in JavaScript is the double equal sign (==), and it returns true if both operands are equal. |
The not equal operator is the exclamation point followed by an equal sign (!=), and it returns true if operands are not equal. |
Both operators do conversions in order to determine if two operands are equal. |
When performing conversions, follow these basic rules: |
- If an operand is a Boolean value, convert it into a numeric value before checking for equality. A value of false converts to 0; whereas a value of true converts to 1.
- If one operand is a string and the other is a number, attempt to convert the string into a number before checking for equality.
- If one operand is an object and the other is a string, attempt to convert the object to a string (using the toString() method) before checking for equality.
- If one operand is an object and the other is a number, attempt to convert the object to a number before checking for equality.
- Values of null and undefined are equal.
- Values of null and undefined cannot be converted into any other values for equality checking.
- If either operand is NaN, the equal operator returns false and the not equal operator returns true.
- If both operands are NaN, the equal operator returns false because, by rule, NaN is not equal to NaN.
- If both operands are objects, then the reference values are compared.
- If both operands point to the same object, then the equal operator returns true. Otherwise, the two are not equal.
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The following table lists some special cases and their results: |
| Expression | Value | | null == undefined | true | | "NaN" == NaN | false | | 5 == NaN | false | | NaN == NaN | false | | NaN != NaN | true | | false == 0 | true | | true == 1 | true | | true == 2 | false | | undefined == 0 | false | | null == 0 | false | | "5" == 5 | true |
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