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JS: Statements & Expressions

Learning Goals

  • Understand the difference between statements and expressions in JavaScript
  • Use various operators in JavaScript

Vocabulary

  • Statement A single piece of code that accomplishes one task or action
  • Expression A statement that produces a value
  • Operator Symbols that are used to assign, compare, and perform operations

Statements

A script is a series of instructions that a computer can follow one-by-one. Each individual instruction is known as a statement. Each statement in JavaScript is followed by a semicolon.

Example statements:

"hello";
358;
false;
console.log('BOOM');
alert('POW');

Expressions

An expression is a statement that, when read by the browser, results in a single value. Expressions can use operators to create this single value. Here are some example expressions:

This expression results in “apple”: "ap" + "ple"

This expression results in 5: 2 + 3

What is the difference?

In simpler terms, a statement performs some kind of action. It does not return anything. An expression produces a value and can be written wherever a value is expected.

Think about the following sentences:

  • “It’s raining a lot!”
  • “It’s raining cats and dogs!”

Both of these sentences are statements! They declare something. But one of them is an expression - it means something other than what the letters actually spell out. “It’s raining cats and dogs” ACTUALLY means “It’s raining a lot”.

Similarly, consider the following code statements:

  • 4;
  • 2 + 2;

They’re both statements. One is an expression - 2 + 2; evaluates to 4;!

Operators

Expressions rely on operators to calculate their single value. There are 5 basic types of operators to get you started:

  1. Assignment operators assign a value to a variable. var color = 'magenta';
  2. Arithmetic operators perform basic math. var addTwo = 2 + 2;
  3. String operators combine strings. var greeting = 'Hello! ' + 'Nice to meet you.';
  4. Comparison operators compare two values and return a true or false. var buy = 3 > 5; // Value of buy is false
  5. Logical operators combines expressions and return a Boolean value of true or false. var buy = (5 > 3) && (2 < 4);

Challenge

Translate each of the following expressions to JavaScript. Type them out in your console so you can be more confident they are doing what you want them to do.

Example: Check if 2 is greater than or equal to 3 Example solution: 2 >= 3

  • Find 12 divided by 3
  • Find the remainder when 12 is divided by 5
  • Combine the strings “hello” and “world” and “!”
  • Check if “4” is the exact same thing as 4
  • Write a variable age and assign to a number. Check if the age is greater than 21 but less than 65.

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