Best javascript syntactic sugar

Object membership test:

var props = { a: 1, b: 2 };

("a" in props) // true
("b" in props) // true
("c" in props) // false

Getting the current datetime as milliseconds:

Date.now()

For example, to time the execution of a section of code:

var start = Date.now();
// some code
alert((Date.now() - start) + " ms elapsed");

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