How do I get a class to return a value?

Question

how does the built in date class work in javascript?

for instance:

var timestamp = new Date('02/14/1994')
// returns milliseconds without having to call timestamp.miliseconds
// it just passes it into the variable

Answer 1

Although your question is not exactly clear on this I suspect you came across something 2 special methods with JavaScript classes that are automatically being called when an object is converted to a string or is compared with another value:

• toString()
• valueOf()

Given the following class we can play around with these:

 class Test { toString() { return 'Hello world'; } valueOf() { return 3; } } const t = new Test(); console.log( t ); console.log( t.toString() ); console.log( `${ t }` ); console.log( t > 2 );

The Date object is very similar here. When you call (new Date()).toString() you will get the full date printed out. If you do cast it into a number with +(new Date()) the internal valueOf() is being used to convert it into its numeric value.