102-06: JavaScript

About JavaScript

• Programming language often seen in web development (among other uses)
• Compiles during execution (“Just-in-Time” computation)
• Can treat functions as variables (“First-Class Functions”) for use by other functions or operations
• Trademarked by Oracle

Input & Outputs

• Can be programmed for client-side inputs to affect the rendered output

Variables

• Use var to define variables and store values, like: var a = 12;
• Variable definitions may refer to other variables, like: ‘var grandtotal = subtotal1 + subtotal2; var subtotal1 = a + b + c; var subtotal2 = x + y + z;`

Identifiers

• Used to store variables
• Naming restrictions: Letters & limited characters (underscore & dollar sign); case-sensitive; some command words excluded

Assignment Operator

• =
• Not an “equals” operation (this is == in JavaScript)
• Can be used to adjust value of stored variable by referring to existing value, like: var x = x +1; to add 1 to the value of the “x” variable

Stored Values

• Numerals
• Text strings (; must be in quotes), like var shave_and_a_haircut = "Two Bits";
• (Not exhaustive list of possible value types)
• Variables may exist without defined value by being declared first, like var Whatsit and can be assigned a value separately from declaration
• Multiple variables may be declared in one line(or several), separated by commas and each after respective assignment operators, like :`var favfood = “Pizza”, favcolor = “Purple”;
• Re-declaration (alone) does not affect stored value
• A numeral in quotes is treated as a text string, as are subsequent numerals in declaration, and will have a value of concatenated digits rather than arithmetic

Variable Interactions

• Arithmetic interactions
• Multiple text strings displayed in order, like var sandwich = "PB" + "J" which outputs sandwich as "PBJ"