JavaScript usually runs one command after another. Sometimes, commands take longer, i.e. HTTP Requests; running them that way will block the whole page. Instead, JavaScript runs these things in a way that calls a function (usually called callback) after the command has finished. However, just calling a function that you receive as an argument leads directly into callback hell:
request1(config,functioncallback1(data){request(data.secondUrl,functioncallback2(data){request(data.thirdConfig,functioncallback3(data){// and so on and so forth});});});
As you can clearly see, this code gets ugly fast. Helpfully, JavaScript now has a class called Promise which helps to make this more manageable:
fetch(config).then((data)=>fetch(data.secondUrl)).then((data)=>fetch(data.thirdConfig))// and so on and so forth
This way, the code becomes much more readable and still does not block the page.
JavaScript usually runs one command after another. Sometimes, commands take longer, i.e. HTTP Requests; running them that way will block the whole page. Instead, JavaScript runs these things in a way that calls a function (usually called
callback) after the command has finished. However, just calling a function that you receive as an argument leads directly into callback hell:As you can clearly see, this code gets ugly fast. Helpfully, JavaScript now has a class called
Promisewhich helps to make this more manageable:This way, the code becomes much more readable and still does not block the page.
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