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Building Front-End Web Applications with Plain JavaScript

Procedures

Explore JavaScript procedures and functions to understand their definitions, invocation, scope, closures, and how methods operate in objects and classes. Learn about anonymous and named functions, arrow expressions, and how to use function methods like call, apply, and bind for effective front-end development.

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What are procedures?

Generally, a parametrized procedure is like a subprogram that can be called with a certain number of arguments any number of times from within a program. Whenever a procedure returns a value, it’s called a function. In OOP, procedures are called methods if they’re defined in the context of a class or an object.

In JavaScript, procedures are called functions, whether they return a value or not. JavaScript functions are special JS objects that have an optional name property and a length property that provide a number of parameters. Whether or not a v variable references a function can be tested as follows:

Javascript (babel-node)
var v = function () { console.log("I am a function.") }
if (typeof v === "function") {
  console.log("true");
}
else {
  console.log("false");
}

A JS object implies that JS functions can be stored in variables, passed as arguments to functions, returned by functions, have properties, and can be changed dynamically. Therefore, JavaScript functions are first-class citizens, and JavaScript can be viewed as a functional programming language.

The general form of a JS function definition is an assignment of a JS function expression to a variable.

var myMethod = function theNameOfMyMethod( params) {
  ...
}

The params variable produces a comma-separated list of parameters (or a parameter record), and theNameOfMyMethod is optional. When it’s omitted, the ...