I am learning JavaScript and I have learned recently about JavaScript timing events. When I learned about setTimeout
at W3Schools, I noticed a strange figure wh
setInterval
or setTimeout
You should pass a reference to a function as the first argument for setTimeout
or setInterval
. This reference may be in the form of:
An anonymous function
setTimeout(function(){/* Look mah! No name! */},2000);
A name of an existing function
function foo(){...}
setTimeout(foo, 2000);
A variable that points to an existing function
var foo = function(){...};
setTimeout(foo, 2000);
Do note that I set "variable in a function" separately from "function name". It's not apparent that variables and function names occupy the same namespace and can clobber each other.
To call a function and pass parameters, you can call the function inside the callback assigned to the timer:
setTimeout(function(){
foo(arg1, arg2, ...argN);
}, 1000);
There is another method to pass in arguments into the handler, however it's not cross-browser compatible.
setTimeout(foo, 2000, arg1, arg2, ...argN);
By default, the context of the callback (the value of this
inside the function called by the timer) when executed is the global object window
. Should you want to change it, use bind
.
setTimeout(function(){
this === YOUR_CONTEXT; // true
}.bind(YOUR_CONTEXT), 2000);
Although it's possible, you should not pass a string to setTimeout
or setInterval
. Passing a string makes setTimeout()
or setInterval()
use a functionality similar to eval() that executes strings as scripts, making arbitrary and potentially harmful script execution possible.
With the parentheses:
setTimeout("alertMsg()", 3000); // It work, here it treat as a function
Without the quotes and the parentheses:
setTimeout(alertMsg, 3000); // It also work, here it treat as a function
And the third is only using quotes:
setTimeout("alertMsg", 3000); // It not work, here it treat as a string
function alertMsg1() {
alert("message 1");
}
function alertMsg2() {
alert("message 2");
}
function alertMsg3() {
alert("message 3");
}
function alertMsg4() {
alert("message 4");
}
// this work after 2 second
setTimeout(alertMsg1, 2000);
// This work immediately
setTimeout(alertMsg2(), 4000);
// this fail
setTimeout('alertMsg3', 6000);
// this work after 8second
setTimeout('alertMsg4()', 8000);
In the above example first alertMsg2() function call immediately (we give the time out 4S but it don't bother) after that alertMsg1() (A time wait of 2 Second) then alertMsg4() (A time wait of 8 Second) but the alertMsg3() is not working because we place it within the quotes without parties so it is treated as a string.
i think the setTimeout function that you write is not being run. if you use jquery, you can make it run correctly by doing this :
function alertMsg() {
//your func
}
$(document).ready(function() {
setTimeout(alertMsg,3000);
// the function you called by setTimeout must not be a string.
});
Totally agree with Joseph.
Here is a fiddle to test this: http://jsfiddle.net/nicocube/63s2s/
In the context of the fiddle, the string argument do not work, in my opinion because the function is not defined in the global scope.
What happens in reality in case you pass string as a first parameter of function
setTimeout(
'string'
,number
)
is value of first param got evaluated when it is time to run (after number
of miliseconds passed).
Basically it is equal to
setTimeout(
eval('string')
,number
)
This is
an alternative syntax that allows you to include a string instead of a function, which is compiled and executed when the timer expires. This syntax is not recommended for the same reasons that make using eval() a security risk.
So samples which you refer are not good samples, and may be given in different context or just simple typo.
If you invoke like this setTimeout(something, number)
, first parameter is not string, but pointer to a something called something
. And again if something
is string - then it will be evaluated. But if it is function, then function will be executed.
jsbin sample
##If i want to wait for some response from server or any action we use setTimeOut.
functionOne =function(){
console.info("First");
setTimeout(()=>{
console.info("After timeOut 1");
},5000);
console.info("only setTimeOut() inside code waiting..");
}
functionTwo =function(){
console.info("second");
}
functionOne();
functionTwo();
## So here console.info("After timeOut 1"); will be executed after time elapsed.
Output:
*******************************************************************************
First
only setTimeOut() inside code waiting..
second
undefined
After timeOut 1 // executed after time elapsed.