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javascriptbooleanbitwise-and

Unusual behaviour with booleans in javascript

While working with booleans in javascript, I have noticed an uncertainty:

"false" && true  //this gives output true
false && true //this gives output false

Can I somebody explain this behaviour?

Solution

  • There's nothing unusual about it. The && operator is short-circuited logical AND. Both conditions need to be true for the entire expression to be true and if any condition is false, the entire operation is false and the rest of the conditions are not tested.

    In the first example, "false" is not the Boolean false, it's the String "false", which is a valid "something", or a "truthy" value, so it evaluates to true.

    console.log("false" && true);  //this gives output true

    In the second example, the actual Boolean false is used, which (as stated) causes the entire operation to be false.

    console.log(false && true); //this gives output false