Intro to coding and software development.
Javascript is integrated with HTML and CSS in a way that it can access content, and modify it, or react to events like user input or perhaps the time of day.
A script is a list of instructions in the JavaScript language. For the most part it is executed in the order it is written from the top of the page to the bottom. An exception to this is a function may be written near the beginning of the script and then called further into the script so that those grouped statements were executed- but after that the execution would return to the place from which the function was called. When planning to write a script, the programmer should first define the goal of the program. Then they should list the steps needed to reach that goal- and those steps should be very simple and literal as the computer will do exactly what it is told to do without any intuitive alteration of the instructions as a human would make.
Espressions are comprised of either assigning a value to a variable, or evaluating two values to produce a single result. For instance the expression var x = 2; would initialize the variable x and assign it the property value of the number two. var sum = x + 10; would calculate what x (in this case it’s 2) plus 10 evaluates into which is 12, and then it assigns the sum variable that value of 12. Operators are ways to manipulate data and include the plus or minus sign, an asterix and foward slash for multiplication and divide respectively, or even an equals sign which we call the ‘asignment operator’ as it will asign a value to a variable. Some operatiors can be used on strings too, it’s not just about numbers! For example var msg = “Hello “ + “World!” would let the variable message contain a single string: “Hello World!”.
A function is one or more statements grouped together, generally because they collectively fulfill some objective of the code. The keyword ‘function’ followed by the name of the function and then two parentheses within which parameters (more on those in a second) may or may not be set and the the curly brackets within which the statements are grouped is the basic structure of a function.
function example(numOne,numTwo) {
var sum = numOne + numTwo;
document.write("The sum of the numbers is: "+sum);
var product = numOne * numTwo;
document.write("The product of the two numbers is: "+product);
}
numOne and numTwo are parameters. They work much like variables but their values can be passed in the statement calling the function. ie: example(3,4); would execute the function which would in turn carry out it’s instructions to add those numbers and assign them to sum, which is written to the document object as 7, and then it would multiply them and assign that to product and then the last statement would write 12 to the document. The curly brackets encapsulate the statements of the function and only get executed if/when the functions gets called. If that function was in a script, but nowhere in the script was there a statement: example(x,y); it would never be used. A further rule to note about functions is that they can not be called earlier in a script than they are declared. In my personal practice I first declare all my global variables at the very beginning of the script, and then I write out all my functions so they are registered by the browser, and after that I put the statements to be run regardless of input or circumstance in the order they should be carried out, and those statements are what typically call upon the functions I’ve defined above the active portion of the script.