JavaScript Timer

Javascript Timer

Timer events

method	description
setTimeout(function, delayMS);	arranges to call given function after given delay in ms
setInterval(function, delayMS);	arranges to call function repeatedly every delayMS ms
setTimeout(timerID); setInterval(timerID);	stops the given timer so it will not call its function

Note : this ID can be passed to clearTimeout/Interval later to stop the timer

Example

Output

After clicking the button Timer start now

 

Passing parameters to timers

function delayedMultiply() {

// 6 and 7 are passed to multiply when timer goes off

setTimeout(multiply, 2000, 6, 7);

}

function multiply(a, b) {

alert(a * b);

}

• any parameters after the delay are eventually passed to the timer function
• Why not just write this? 

setTimeout(multiply(6 * 7), 2000);

Common timer errors

setTimeout(booyah(), 2000);

setTimeout(booyah, 2000);

setTimeout(multiply(num1 * num2), 2000);

setTimeout(multiply, 2000, num1, num2);

• what does it actually do if you have the () ?
• it calls the function immediately, rather than waiting the 2000ms!