kofodym / jsarrayfunctions

Simple JavaScript files to display elements within an array , in a function and outside a function.

Article Summary

JavaScript Array Methods

Examples are:

• Array length: This property returns the length (size) of an array. e.g let size = fruits.length;

• Array toString(): This toString() converts an array to a string of (comma separated) array values.e.g fruits.toString();

• Array pop(): The pop() method removes the last element from an array. e,g fruits.pop()

• Array push(): The push() method adds a new element to an array (at the end). e.g. fruits.push("Kiwi")

• Array shift(): The shift() method removes the first array element and "shifts" all other elements to a lower index. e.g. fruit.shift();

• Array unshift(): The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements. e.g. fruit.unshift("Kiwi");

• Array splice(): The splice() method adds new items to an array. e.g fruits.splice(2, 0, "Lemon", "Kiwi");

  • The first parameter (2) defines the position where new elements should be added (spliced in).
  • The second parameter (0) defines how many elements should be removed.
  • The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.

• Array slice(): The slice() method slices out a piece of an array and returns an array with the deleted items.e.g. fruits.splice(2, 2, "Lemon", "Kiwi");

• Array join(): The join() method also joins all array elements into a string, but in addition you can specify the separator. e,g. fruits.join(" \* ")

• Array delete(): Using delete leaves undefined holes in the array. e. g delete fruits[0]. Its better to Use pop() or shift() instead.

• Array concat(): The concat() method creates a new array by merging (concatenating) existing arrays. e.g myGirls.concat(myBoys) , arr1.concat(arr2, arr3); , arr1.concat("Peter") . Note: The concat() method does not change the existing arrays. It always returns a new array.

• Array flat(): Flattening an array is the process of reducing the dimensionality of an array. e.g const myArr = [[1,2],[3,4],[5,6]]; , const newArr = myArr.flat();

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JavaScript Functions

A JavaScript function is a block of code designed to perform a particular task.

A JavaScript function is executed when "something" invokes it (calls it).

• A JavaScript function is a block of code designed to perform a particular task.

• A JavaScript function is executed when "something" invokes it (calls it).

Function Invocation

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JavaScript Reference Functions

Functions are first-class objects, because they can be passed to other functions, returned from functions, and assigned to variables and properties. 

Values can be passed to a function as parameters, and the function will return a value.

Return value

• One function call can only return one value, but you can simulate the effect of returning multiple values by returning an object or array and destructuring the result.

Passing arguments

• Arguments are always passed by value and never passed by reference. This means that if a function reassigns a parameter, the value won't change outside the function.

Function parameters

Function parameter is a simple identifier that you can access in the local scope.

Defining functions

Broadly speaking, JavaScript has four kinds of functions:

• Regular function: can return anything; always runs to completion after invocation
• Generator function: returns a Generator object; can be paused and resumed with the yield operator.
• Async function: returns a Promise; can be paused and resumed with the await operator
• Async generator function: returns an AsyncGenerator object; both the await and yield operators can be used

For every kind of function, there are three ways to define it:

• Declaration
• Expression
• Constructor

Block-level functions

• functions inside blocks are scoped to that block.

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JavaScript Control Flow Statements

In JavaScript, there are three main types of control flow statements:

• if/else statements: The if…else statement executes a block of code if a specified condition is true. If the condition is false, another block of code can be executed.
• switch statements: Switch statements are used to execute a block of code based on the value of a variable or expression.
• Loops.
  • For Loops
  • While Loops : A while loop simply repeats itself while something is true. It continues until the condition is false.
  • do ... while loop : The do ... while loop will first execute the code, then continue while the condition remains true.

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JavaScript Functions Basics

• Functions are the main “building blocks” of the program. They allow the code to be called many times without repetition.

To create a function we can use a function declaration.

function showMessage() {
 alert( 'Hello everyone!' );
}
showMessage().

Local, Outer,and Global variables

• Local variables declared inside a function is only visible inside that function.
• The function has full access to the outer variable. It can modify it as well.
• Global variables are visible from any function.

Parameters

• Parameters are arbitrary data passed to a function.
• An argument is the value that is passed to the function when it is called (it’s a call time term).

Default values

• If a function is called, but an argument is not provided, then the corresponding value becomes undefined. e.g showMessage(from, text) called with showMessage("Ann"); l would output *Ann*: undefined"
• We can specify the so-called “default” (to use if omitted) value for a parameter in the function declaration, using =. e.g showMessage(from, text = "no text given")
• To check if parameter is missing use ??

Return a value

• When the execution reaches a return, the function stops, and the value is returned to the calling code.
• If a function does not return a value, it is the same as if it returns undefined