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11-functions-built-in.md

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Functions - Built in

  • Function allows us to group together multiple statements, take in some values, perform some operations and return some value.

  • Functions take in data known as arguments.

  • Function may or may not return a value.

  • Example:

      Math.max(10, 12); // 12

    The above line is a JavaScript statement.

    10 and 12 passed to the function are arguments, separated by comma.

    12 is returned from the function.

  • There are many in-built JavaScript functions.

    e.g:

    • console.log('hey'); returns undefined , logs hey.
    • parseFloat('2.032565') // 2.032565 (converts string to number)
    • parseInt('2.032565') // 2 (converts string to number as integer)
    • Many date functions are also present. e.g. Date.now() returns no. of milliseconds since January 1, 1970 00:00:00 UTC.
    • DOM functions:

      • Example:

          <body>
  <p>Hey How ya doin?</p>
  	<script>
  		const para = document.querySelector('p'); // finds p tag in page
  		console.log(para); // <p>Hey How ya doin?</p>
  	</script>
  </body>

      • Mobile only functions e.g. navigator.vibrate()

  • In case of doubts, always refer MDN Docs.

  • Other Examples:

      scrollTo(0, 200); // scrolls to (x, y) position in page
  
  scrollTo({
  	top: 500,
  	left: 0,
  	behavior: 'smooth'
  }); // scrolls to position top: 500, left: 0 in a 'smooth' manner

    The scrollTo function returns undefined.