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Dynamic Web Pages with Javascript

Javascript

javascript is a lightweight compiled programming language with first-class-functions. It is, in fact, not related to java and they are two very different languages.

Input Output

an example of how to get input from a user

first name: <input id="first_name"> last name: <input id="last_name"> <button id="say">Say hi!</button> <div id="result"></div> <script> function say_hi() { var fname = document.getElementById('first_name').value; var lname = document.getElementById('last_name').value; var html = 'Hello <b>' + fname + '</b> ' + lname; document.getElementById('result').innerHTML = html; }

document.getElementById('say').addEventListener('click', say_hi); </script>

JavaScript Variables

you can declare a variable using

• var
• let
• const
• or nothing

variables are containers for data values.

When to Use Var vs Const vs Let

let and const are more recent additions than var, so if you’re coding for an older browser, var should be used. Otherwise, const should be used for general rules and let should be used if the value of the variable is likely to change.

Javascript Identifiers

all javascript variables must be identified with unique names, which can be a single character or something more descriptive.

• names can contain letters, digits, underscores, and dollar signs
• names must begin with a letter, $, or _
• names are case sensitive
• reserved words cannot be used as names

The Assignment Operator

= is used to assign a value to a variable.

JavaScript Data Types

javascript variables can hold number and text strings. To differentiate for the variable assignment, strings are placed in quotations and numbers are not.

Declaring a JavaScript Variable

var nameHere is the correct way to declare a variable with no value. You can then assign it value afterwords using = or you can assign it while you’re declaring it. You should generally declare all variables at the beginning of your script

One Statement, Many Variables

you can declare as many variables as you want in one line as long as they’re separated by a comma.

Re-Declaring JavaScript Variables

if you re-declare a variable with the same name, it will still have the same contents.

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