Why Is My Function Call That Should Be Scheduled by Settimeout Executed Immediately

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Why Is My Function Call That Should Be Scheduled by Settimeout Executed Immediately

#Why Is My Function Call That Should Be Scheduled by Settimeout Executed Immediately| 来源: 网络整理| 查看: 265

Why is the method executed immediately when I use setTimeout?

You're calling the function immediately and scheduling its return value.

Use:

setTimeout(testFunction, 2000); ^

Notice: no parens.

Why is setTimeout executing immediately?

because you're actually calling the timeup(tc,chosen) function inside the setTimeout function.

try:

setTimeout(function(){ timeup(tc,chosen);}, 10000); setTimeout -- callback executed immediately?

Several problems.

This invokes hide_info right away. Parenthesis invoke a function-object! (or are used for applying precedence to expressions).

That is,

this.id = setTimeout(this.hide_info(), 7000);

Is [mostly] equivalent to:

var temp = this.hide_info() // call function ... uh, what?this.id = setTimeout(temp, 7000) // temp is "return" value ("undefined" here)

Oops! That's not right :) So take away the parenthesis. This will pass the function-object itself to the setTimeout. (Yes, functions are just objects in JavaScript. The expression this.hide_info is first evaluated to a function-object and, if there is a (...) after, it will invoke said function-object.)

this.id = setTimeout(this.hide_info, 7000)

However, it is still not correct because this inside the timeout function (hide_info) will be wrong! But this can be fixed with using a closure. (There are many great SO answers on the topic, feel free to search!)

var self = thisthis.id = setTimeout(function () { // now in hide_info "this" will be "self", which was "this" ... outside :) self.hide_info()}, 7000)

(Or use Function.bind from ECMAScript ed5 or a library.)

Additionally, this.id is not the same as this.timeoutID, and is suspect for "correctness".

Keep it simple. It's okay to pass undefined/0 to clearTimeout: it'll silently ignore you.

cancel : function () { clearTimeout(this.id) // but id is a horrid overloaded name :) this.id = undefined}

Happy coding.

setTimeout runs immediately

That is because you are calling the function "function(elem)" instead of providing it as an arguement. Try this

setTimeout takes as the first parameter a function, alice.sayHi.call(bob) is not a function, it's undefined (it is the returned value of the function, not the actual function).

So you need to specify a callback instead, wrap your function inside another one like so:

I thought I would mention that if those test() calls do not perform DOM operations you could possibly move them to a worker.

Web Workers allow running code on a background thread that doesn't block your main UI thread.I've created a quick example that runs a synchronous task of arbitrary duration on a worker thread. On the main thread setInterval and setTimeout calls are running uninterrupted.

See it in action.

index.js

let interval = setInterval(() => console.log("Not blocked"), 500);

console.log("Scheduling to run in 2 seconds");setTimeout(() => { console.log("2 seconds passed. Running scheduled task! ");}, 2000);

let longTaskRunner = new Worker("./src/worker.js");let taskDuration = 3;console.log( `Starting synchronous task that takes more than ${taskDuration} seconds`);

longTaskRunner.postMessage(taskDuration);longTaskRunner.onmessage = function(e) { console.log(`Long task completed in ${e.data} seconds`); clearInterval(interval);};longTaskRunner.onerror = function(e) { console.log(e.message);};

worker.js

self.onmessage = function(e) { const runFor = e.data * 1000; let startedAt = Date.now(); let timeElapsed = 0;

while (timeElapsed < runFor) { timeElapsed = Date.now() - startedAt; }

self.postMessage(timeElapsed / 1000);};

setTimeout firing function straight away and not waiting

Your function getNegativeErrs() is executing right away and is using its return value as the callback.

The right way:

window.setTimeout(function() { getNegativeErrs(errors) }, 5000);

function getNegativeErrs(ers) { for( i in errors ) { var errobj = getByValue(dataLayer, errors[i]); if(!errobj) { dataLayer.push({ 'event': 'negative_errors', 'unseen': errors[i], 'module': 'registration' }) } } }