Clash Royale CLAN TAG#URR8PPP

Adding a parameter to a function in .then() breaks the behaviour of a promise in JS

getPosts() loops through an array of posts, builds LIs and places them inside document.body. Works ok.

function getPosts(num)
let output ='';
posts.forEach((post, index)=>
output += `<li>$post.title ($num)</li>`;
);
document.body.innerHTML += output;



createPost() returns a promise which waits 3 seconds (to simulate client-server delay), adds a post to the array and resolves.

function createPost(post)
return new Promise((resolve, reject) =>
setTimeout(()=>
posts.push(post);
const error = false;
if (error)
reject ('Error happened!');
else
resolve();

,3000);
);



The following works as expected. Three LIs are returned, with (undefined):

createPost (title: 'Post Three', body: 'Post Three')
.then(getPosts);


But when getPosts inside .then has a parameter, it is fired without waiting for promise to resolve:

createPost (title: 'Post Three', body: 'Post Three')
.then(getPosts(1));


Why?

https://codepen.io/Marko36/pen/LJoRYN

1 Answer
1

In your then you give a callback function.

then

then(getPosts) will be called with the argument given: getPosts(result)

then(getPosts)

getPosts(result)

But getPosts(1)is immediately resolved.

getPosts(1)

What you want is ()=> getPosts(1)

()=> getPosts(1)

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