An expression is a valid unit of code that resolves to a value. All complex expressions are joined by operators. There are two (2) types of expressions: those with side effects (like assigning values) and those that only evaluate.
x = 7
= operator to assign a value of 7 to the variable x.3 + 4
The precedence of operators determines the order that they are applied when evaluating an expression. Arithmetic operators seem to follow normal order of operations learned in introductory math classes. For a complete table of operator precedence and exceptions to the rules please refer to the Operator Precedence page.
An assignment operator assigns a value to its left operand based on the value of the right operand. A simple assignment operator is = which assigns the value of its right operand to the left operand. To explain, in the expression x = f(), the value of f() is assigned to x. There are also compound assignment operators which are shorthand for mathematic operations.
A comparison operator compares operands and returns a logical value based on whether the comparison is “true”.
Loops are functions that provide a quicky and easy way to perform an action repeatedly. There are many types of loops, but they all have a similar function: repeat an action some ‘i’ number of times (the number could be 0 or infinity)
A for loop repeats until a specified condition evaluates to false. Useful when the programmer knows or expects how many steps/actions will be needed.
Structure:
for
for(initial value; condition to evaluate; increment){code to execute}
Example 1
for (let i = 0; i < 3; i++){
console.log(i);
}
| Initial Value | Logic Evaluation | Code to Execute | Next Value |
|---|---|---|---|
| i = 0 | 0<5? True | console.log 0 | i is 1 |
| i = 1 | 1<5? True | console.log 1 | i is 2 |
| i = 2 | 2<3? True | console.log 2 | i is 3 |
| i = 3 | 3<3? False | BREAK LOOP | N/A |
Example 2
function rateMyPage(){
let rating = prompt("How many starts would you rate my page?");
for (let i = 0; i < rating; i++){
document.write("STAR");}
Used when we don’t know how long something will take or how many loops we want. A while statement is executed as long as a condition evaluates to true.
Structure:
while
while (condition to evaluate is true){execute this code}
console.log(!false); = not false = true
console.log(!true); = not true = false
Loop will continue until input is “yellow”
let response = prompt("What is my favorite color?");
while (response !== 'yellow'){response = prompt("Wrong, guess again");
}
console.log("Congrats, you guessed it!");
Example of self limiting loop
let x = 0;
while(x < 100){
console.log(x);
x++;}