如何循环遍历数组以等待每个项目之间的时间？

Question

I have an array like this:

var items = [["text1", 3000],["text2",4000],["text3",1000]], ...a lot more here...; .

In the html side, we got <div id="d"></div>

Now, I want to print out " text1 " on the div after 3000 milliseconds, the PC will then wait for 4000 milliseconds before printing " text2 ", then it will print out " text3 " after 1000 milliseconds, so on until it finishes the loop.

I think we need to do with setInterval or something like that but it is too hard for me to think of it. Maybe a nested setInterval ??

So Given an 2-D array of text & millisecond-number, How to print each item out after a specified milliseconds?

Note: I need to print out in the right order of items , that is it will print out text1 first, then text2, then text3, ...

Answer 1

Edit

Finally found the solution

 var items = [["text1", 3000],["text2",4000],["text3",1000]]; var time=0; printElems(0); function printElems(i){ setTimeout(function(){ var elem=document.getElementById("d"); elem.innerHTML=items[i][0]; if(items[i+1]!=undefined){ printElems(i+1); } },items[i][1]); }

 <div id="d"></div>

This will do the trick. What I have done here is, just sum the times and make setTimeout calls based on the delay.This loops through the array in the given order.

Answer 2

Unfortunately, they will be printed from the shortest time to the longest time if you wrap a setTimeout (asynchronous) in a loop (synchronous).

To solve the problem you can use Promises.

Here is an implementation with jQuery.Deferred :

var dfd = $.Deferred().resolve();

items.forEach((item) => {
    dfd = dfd.then(() => print(item));
});

function print(item) {
    var dfd = $.Deferred();

    setTimeout(() => {
        $('#d').html(item[0]);
        dfd.resolve();
    }, item[1]);

    return dfd.promise();
}

DEMO

Answer 3

With promises, compactly:

function wait(ms) { return new Promise(resolve => setTimeout(resolve, ms)); }

items.reduce((promise, [text, ms]) => 
    promise . then(() => wait(ms)) . then(() => console.log(text)),
  Promise.resolve());

With setTimeout , recursively:

function sequence(array) {
  if (!array.length) return;
  var elt = array.shift();
  setTimeout(() => {
    console.log(elt[0]);
    sequence(array);
  }, elt[1]);
}