using setTimeout on promise chain

Question

Here i am trying to wrap my head around promises Here on first request i fetch a set of links and on next request i fetch the content of first link But i want to make a delay before returning next promise object So i use setTimeout on it But it gives me the following JSON error  without setTimeout   it works just fine      SyntaxError  JSON parse  unexpected character at line 1 column 1 of   the JSON data   i would like to know why it fails   let globalObj     function getLinks url       return new Promise function resolve reject           let http   new XMLHttpRequest           http onreadystatechange   function                if http readyState    4                 if http status    200                   resolve http response                  else                  reject new Error                                                              http open  GET  url true          http send               getLinks  links txt   then function links       let all links    JSON parse links        globalObj all links       return getLinks globalObj  one     txt        then function topic         writeToBody topic       setTimeout function             return getLinks globalObj  two     txt       without setTimeout it works fine             1000

User · Answer

If you are inside a  then   block and you want to execute a settimeout                 then      gt                    console log  wait for 10 seconds                             return new Promise function resolve  reject                         setTimeout      gt                            console log  10 seconds Timer expired                               resolve                           10000                                                  then      gt                    console log  promise resolved                         output will as shown below  wait for 10 seconds         10 seconds Timer expired    promise resolved      Happy Coding

User · Answer

The shorter ES6 version of the answer   const delay   t   gt  new Promise resolve   gt  setTimeout resolve  t      And then you can do   delay 3000  then      gt  console log  Hello

User · Answer

then      gt  new Promise  resolve    gt  setTimeout resolve  15000     UPDATE  when I need sleep in async function I throw in await new Promise resolve   gt  setTimeout resolve  1000

User · Answer

In node js you can also do the following   const   promisify     require  util   const delay   promisify setTimeout   delay 1000  then      gt  console log  hello

User · Answer

To keep the promise chain going  you can t use setTimeout   the way you did because you aren t returning a promise from the  then   handler - you re returning it from the setTimeout   callback which does you no good     Instead  you can make a simple little delay function like this   function delay t  v       return new Promise function resolve            setTimeout resolve bind null  v   t             And  then use it like this   getLinks  links txt   then function links       let all links    JSON parse links        globalObj all links       return getLinks globalObj  one     txt        then function topic       writeToBody topic          return a promise here that will be chained to prior promise     return delay 1000  then function             return getLinks globalObj  two     txt                  Here you re returning a promise from the  then   handler and thus it is chained appropriately     You can also add a delay method to the Promise object and then directly use a  delay x  method on your promises like this    x000D   x000D  function delay t  v    x000D     return new Promise function resolve     x000D         setTimeout resolve bind null  v   t  x000D         x000D    x000D   x000D  Promise prototype delay   function t    x000D      return this then function v    x000D          return delay t  v   x000D          x000D    x000D   x000D   x000D  Promise resolve  hello   delay 500  then function v    x000D      console log v   x000D      x000D   x000D   x000D    Or  use the Bluebird promise library which already has the  delay   method built-in

[javascript] using setTimeout on promise chain

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