Javascript Loops
Javascript loops are control structures that allow for the repetition of a block of code. Common types of loops in Javascript include the "for" loop, "while" loop, and "do-while" loop. These loops are used to iterate through arrays, manipulate data, and perform repetitive tasks, making them essential for efficient programming in Javascript.
6 Key excerpts on "Javascript Loops"
eBook - ePubConfident Web Design
Master the Fundamentals of Website Creation and Supercharge Your Career
- Kenny Wood(Author)
- 2018(Publication Date)
- Kogan Page(Publisher)
...They are a way to run a piece of code multiple times as per your requirements. They are often used alongside arrays, but their uses span far beyond just working with arrays. There are four different types of loops in JavaScript. The most common loop you will see is the ‘for loop’. Let’s take a closer look at this loop now. The for loop The for loop is a very common loop, which simply runs a section of code a defined number of times. Here’s how it works: for(statement 1; statements 2; statement 3) { } This is the basic structure of the for loop. We start with the keyword ‘for’, followed by three statements, which define how many times our loop runs. Statement 1 is a piece of code you will write that will be run BEFORE the loop runs. Statement 2 is a condition statement, which will decide whether or not the loop should run. Statement 3 is a piece of code you will write that will be run AFTER your code inside the loop is run. Let’s look at an example and break down exactly how it all works: for(var i = 0; i < 10; i++) { console.log(i); } The above loop will run for 10 times exactly and then stop. Here’s what’s going on here: Var i = 0 This code declares a variable called i, and sets it equal to 0. This code runs before any loops are run. This section is only ever run once at the start of the loop process. i < 10 The loop then checks this statement to see if it returns true. This statement in question is ‘is the variable i less than the value 10?’. Because our variable i is set to 0, this will return TRUE, and so the loop will run. The statement here is what’s known as a condition. We will explore more about conditions later. i++ After the block of code inside the curly brackets is run, this is then executed. Remember when we see this i++ it is an arithmetic operation, that is the equivalent to i = i + 1. The code here simply adds 1 to our i variable...
eBook - ePub- Mike McGrath(Author)
- 2020(Publication Date)
- In Easy Steps Limited(Publisher)
...Both while loops and for loops are sometimes referred to as “pre-test” loops because their test condition is evaluated before any statements are executed. A while loop can be made to perform a specific number of iterations, like a for loop, by using a counter variable as the test condition and incrementing its value on each iteration. For example, a while loop structure to execute a set of statements 100 times might look like this: let i = 0 while (i < 100) { statements-to-be-executed i++ ; } The counter variable is incremented on each iteration until its value reaches 100, upon which the evaluation returns false and the loop ends. Omitting a modifier from the while loop structure will create an infinite loop that will run forever. Create an HTML document with a self-invoking function that begins by initializing a loop counter variable let i = 10 while.html Next, insert a while loop structure that will make iterations and output the value of the loop counter on each iteration until it reaches zero while(i > -1) { console.log(‘ Countdown Number: ‘ + i) i -- } Save the HTML document, then open it in your browser and launch the console to see the loop iterations Each while loop must have braces as they contain at least two statements – one statement to execute and a modifier. Do Loops Another kind of loop available in JavaScript is. the do while loop structure. This is like an inverted version of the while loop, described here, and is ideal when the statements it will execute on each iteration absolutely must be executed at least one time. Its syntax looks like this: do { statements-to-be-executed modifier } while (condition) The parentheses after the while keyword contain a condition that is evaluated for a boolean value after each iteration. Statements to be executed on each iteration are enclosed within braces along with a statement that modifies a value in the test condition, so that at some point its evaluation will return false and the loop will exit...
eBook - ePubCoding + Math
Strengthen K–5 Math Skills With Computer Science
- Nicol R. Howard(Author)
- 2020(Publication Date)
...However, conditionals can also be modeled effectively through the use of flowcharts or unplugged programming activities. Loops Loops are a mainstay of programming, allowing far more efficiency in programming tasks that must be repeated until a desired result is achieved. For example, if a programmer wants the program to perform a task repeatedly a certain number of times but wants the user to determine that number at runtime, the code would utilize a “for-loop”, accepting user input to set the number of intervals. In Scratch terminology, the coder could use an “ask” block to get user input on how many times the sprite should follow a certain sequence. In that case, the code would contain a “repeat” block to encapsulate the loop containing the blocks in the sequence. This not only prevents the need for repetitive code, but also avoids restricting the loop to some predetermined maximum number of iterations. While loops provide additional power and flexibility to the programmer, they also present a source of potential errors if not used properly. Research has shown the use of endless loops in the Scratch environment as a source of many programming errors, where programs get stuck in never-ending loops (Zhang & Nouri, 2019). Varied understanding of different types of loops, particularly nested loops, have often caused confusion, but this confusion has been less prevalent for Scratch users as compared to text-based languages, since loops are easier to identify in a block-based environment (Mladenovi et al., 2017). Perhaps the best analogy for loops in math is summation notation (∑ 2 i, e.g., meaning the summation of all values of 2 i, starting with 1 and ending with 10); this concept is usually not covered until secondary school...
- Kenneth J. Luterbach(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...grade. Iterative Statements An iterative statement creates a loop, which enables the repeated execution of a set of statements. At times, programmers include an iterative statement within an iterative statement (or loop within a loop), which we will do after mastering straightforward loops. Repetition a Fixed Number of Times for (i = 1; i <= 7; i++) {// loop body print(i); } The for loop above displays the numbers 1 through 7, each on a separate line. Initially, the loop control variable, i is set to 1. As long as i is less than or equal to 7, the statement or statements in the loop body are executed. Since braces {} surround the loop body, any number of statements can be included in the loop body. Run the for loop above in the JavaScript shell. Type the first line and hold down the Shift Key before pressing the Enter or Return key. In that way, the first line will not be executed yet. Then type the second line and again hold down the Shift Key before pressing the Enter or Return key. Lastly, enter the final closing brace } and press the Enter or Return key. Alternatively, you could enter the code into your text editor, then save and run. Once you have that loop working, editor and enter the following code in lates the sum of a set of numbers. Save open a new document in your text order to create a program that calcuthe file as nwnberCmnclierl.js. sum = 0; for (i = 1; i <= 5; i++) { print ("Enter a number to include in the sum"); currentNumber = readline(); sum = sum + currentNumber; } print("The sum is " + sum); Task 3.1 Enhance the numberCruncher1.js by also calculating and displaying the mean, which in this case is the sum divided by five (i.e., sum / 5). Task 3.2 Always calculating the sum of five numbers is a severe limitation. Before the loop begins in numberCruncher1.js, prompt the user to enter the population size, N, which is the number of numbers to be summed...
eBook - ePubTradeStation Made Easy!
Using EasyLanguage to Build Profits with the World's Most Popular Trading Software
- Sunny J. Harris(Author)
- 2011(Publication Date)
- Wiley(Publisher)
...Chapter 11 Loops In This Chapter Introduction For While INTRODUCTION A loop is just as it sounds; it goes around and around until you tell it to stop. A loop defines a group of instructions that will continue executing until a condition is met. The condition being met will cause the loop to stop. A FOR loop will execute a predefined number of times. The predefined number of times is the condition. A WHILE loop will continue to execute while (as long as) the condition is true. Loops allow you to calculate something over a range of values, such as from 1 to 10. Or to take action only while a condition is met, such as: while it is the month of October, only take short trades. Loops allow you to calculate averages, and summations and even count backward. As your programming skills become more proficient, you will find yourself discovering more and more uses for loops. FOR TEMPLATE 1 FOR Value1 = m TO n BEGIN … END; TEMPLATE 2 FOR Value1 = m DOWNTO n BEGIN … END; The FOR command always appears with a BEGIN … END block and is sometimes referred to as a FOR … BEGIN command. The FOR command is always followed by a set of variables that define the starting and ending number of steps to execute the loop. This structure is pretty complex until you get accustomed to it; then it will become second nature, so don’t start worrying yet. Templates for these concepts are shown above. You will specify m and n, and provide code for your task in place of the... s. FOR is always followed by a variable name (Value1 in Figure 11.1). The command tells the computer to perform a set of actions a specified number of times. The variable counts the number of times as it steps through the loop...
eBook - ePubHack Audio
An Introduction to Computer Programming and Digital Signal Processing in MATLAB
- Eric Tarr(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...As a matter of best practice, a programmer should use the loop statement that allows for the easiest interpretation of the written code. When the number of repetitions in the loop can be explicitly set prior to the loop, it is often preferred to use the for statement. When the number of repetitions cannot be known, it may only be possible to use the while loop. Examples: Create and run the following m-file in MATLAB. % This script compares the process of using a for loop % with the process of using a while loop. The same % result can be accomplished with each type of loop by using % the appropriate syntax. % for loop example N = 4; % Number of elements for signal sig1 = zeros(N,1); % Initialize an output signal for ii = 1:N sig1(ii) = sin(ii*pi/2); % Fill the output array % with values from the end % sine function sig1 % Display result on Command Window % while loop example sig2 = zeros(N,1); % Initialize new output signal jj = 1; % Declare a counting variable while jj ≤ N sig2(jj) = sin(jj*pi/2); % Fill the output array jj = jj + 1; % Iterate counting variable end sig2 % Display result on Command Window Example 5.13: Script: simpleLoop.m In audio signal processing, for loops are a common way to iteratively step through each. sample of a signal. For many signals in MATLAB, the number of samples can usually be determined. Then, the loop can be set to index through the individual samples or segments of the entire signal. 5.3.3 Functions Functions are a set of commands grouped together and executed each instance the function is called. MATLAB has many built-in functions including sqrt, sin, cos, ceil, and so on. Functions may have input and output variables, but they are only necessary if required by the particular function. Input variables to functions are enclosed in parantheses after the function name. Multiple input variables are separated by commas. Output variables from functions are enclosed in square brackets to the left of an equal sign and function name...
