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Basic Program Structure

The basic structure of a JavaScript script or program

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Basic Program Structure

Expression: A fragment of code that makes a value. Can be nested inside each other, or just be literal values.

Bindings: Values need to be bound to something or they will be lost. This is done be assigning them to variables. An example is let variable = 10 + 10.

Environment: Collection of all bindings available at any given time. Includes defaults used even in empty programs.

Functions: Pieces of a program wrapped in a value. * Run the code in a function by invoking it, usually with parenthesis after the value name. Example: example_function(). * Functions can use different values when run, which are arguments and put in the parenthesis. * Some functions have side effects, or direct effects on other code. Others instead simply return values that are used elsewhere.

Control Flow: Problems with many lines execute each line one after the other, like a story. * Sometimes there’s conditional execution, where code takes a certain path depending on some parameters. This can be done with an if statement that executes or skips a section of code if an expression is true or false. * One way to manage control flow is the isNaN function included in JS. If the given argument isn’t a number, such as isNaN(44), then it skips the code. If it works, such as with isNaN("string"), it runs the code.

Block syntax for if statement:

if (isNaN("string")) {
    console.log("Not a number!")
    console.log("How dare you.")
}

Statement syntax for if statement (only if one statement returned):

if (isNaN("string")) console.log("Not a number! How dare you.")

The if statement can also use else if and/or else for chaining conditions:

let num = Number(prompt("Pick a number"));

if (num < 10) {
  console.log("Small");
} else if (num < 100) {
  console.log("Medium");
} else {
  console.log("Large");
}