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GeezerVison is showing javascript.info — A question about "if"

A question about "if"

importance: 5

Which of these alerts are going to execute?

What will the results of the expressions be inside if(...)?

if (-1 || 0) alert( 'first' );
if (-1 && 0) alert( 'second' );
if (null || -1 && 1) alert( 'third' );

The answer: the first and the third will execute.

Details:

// Runs.
// The result of -1 || 0 = -1, truthy
if (-1 || 0) alert( 'first' );

// Doesn't run
// -1 && 0 = 0, falsy
if (-1 && 0) alert( 'second' );

// Executes
// Operator && has a higher precedence than ||
// so -1 && 1 executes first, giving us the chain:
// null || -1 && 1  ->  null || 1  ->  1
if (null || -1 && 1) alert( 'third' );

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