FUNCTIONS A function is basic building block. In functional programming language, everything is done using functions. but pure function needed. a function is of two type: pure function and impure function. In pure function, it wont effect immutable and mutable function otherwise it will be impure function Example 1: function hi(){ console.log('I am inside hi'); } hi() Example 2: IIFE (immediately invoke functional expression) ()() Example 3: (function(){ console.log('I am anonymous function'); })(); Example 4: function sendMail(option){ //mail send function console.log('Option is', option); var sinuna = option.email; var to = option.to; var santoo = option.sub; var text = option.msg; option.email = 'info@fascinating.com' return true; return '...
Source: https://www.geeksforgeeks.org/javascript-promises/ Promise is easier than callback because code is readable in promise. Promise has also a method. Methods: then, catch, finally (these methods use callback) Benefits of Promises Improves Code Readability Better handling of asynchronous operations Better flow of control definition in asynchronous logic Better Error Handling A Promise has four states: fulfilled : Action related to the promise succeeded rejected : Action related to the promise failed pending : Promise is still pending i.e not fulfilled or rejected yet settled : Promise has fulfilled or rejected
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