Multiplication with date object - javascript

Question

I came across this piece of code var timeStamp = 1 * new Date(); and to my surprise it returned value in milliseconds since 1970/01/01. This is equivalent to us

Answer 1

Numeric conversion

It is because of numeric conversion in javascript which is almost same like toString but internally it is called much more often.

Numeric conversion is performed in two main cases:

• In functions which needs a number: for example Math.sin(obj), isNaN(obj), including arithmetic operators: +obj.
• In comparisons, like obj == 'John'. The exceptions are the string equality ===, because it doesn’t do any type conversion, and also non-strict equality when both arguments are objects, not primitives: obj1 == obj2. It is true only if both arguments reference the same object.

The explicit conversion can also be done with Number(obj).

The algorithm of numeric conversion:

• If valueOf method exists and returns a primitive, then return it.

• Otherwise, if toString method exists and returns a primitive, then return it.

• Otherwise, throw an exception.

Among built-in objects, Date supports both numeric and string conversion:

alert( new Date() ) // The date in human-readable form
alert( 1*new Date() ) // Microseconds from 1 Jan 1970

Further reading