Leerlog JavaScript

Table of Contents

• Basic functions
• Strings I
  • Strings
  • Character access
  • Substrings
  • Plus operator
  • Template strings
• Numbers
  • Numbers
  • Convert string to number
  • Operations
• Variables
• Conditions
  • Conditions

Basic functions

• In JavaScript, you have to return from inside functions. If you forget to write return, your function will return undefined
• The return keyword will also quit/exit the function.

Strings I

Strings

• You can create strings with ” or ’
• .length is a property that gives you the length of a string
• .toUpperCase() is a function that converts the string to upper case
• .toLowerCase() is a function that converts the string to lower case
• parentheses () on function calls are required. .length is a property that is already pre-computed; therefore, it does not need parentheses.
• console.log(...) is used for debugging and is NOT a replacement for return.

Character access

• Square brackets [index] are used to access a specific index from a string.
• The index starts at 0. So the first character is index 0.
• You can combine it with the length of a string to get another character in another position.
• The .at() method allows you to read a character at an index (which can also be negative).

Substrings

• A substring is a part or a portion of a string.
• string.substring(indexStart, indexEnd) is used to return a portion of the string.
• indexStart: the position of the first character you’d like to include.
• indexEnd: the position of the first character you’d like to ignore.
• The indexEnd argument is optional which means you can leave it out.

Plus operator

• The + operator is used to add 2 numbers
• The + operator is used to concatenate 2 strings
• You can rewrite the name = name + in a shorter way using the += operator: name += " Blue"

Template strings

• A template string is a string created with the backtick character: `
• Template strings can span multiple lines
• Template strings support interpolation with the ${variableName} syntax

Numbers

Numbers

• Convert from a number to string: value.toString()
• NaN stands for Not a Number
• NaN is often a sign of a bug.

Convert string to number

• Convert from string to number Number.parseInt(value, 10).
• Number.parseInt() is the name of the function you’re calling.
• 10 is the radix which you should specify.
• Make sure to always specify the radix to avoid unpleasant surprises.

Operations

• The remainder operator (%) returns the division remainder between 2 numbers.
• While there are some other methods you could call on numbers, they are not very commonly used. What is commonly used, however, is the Math object which contains methods such as min(), max(), round(), etc.

Variables

• When you use a variable for the first time in JavaScript, you need to declare it with either let or const.
• Use let for variables that you will need to re-assign later on (as in changing their value)
• Use const for variables that you won’t need to re-assign later on.
• Variables declared with const are not constant. We will see why later in this course.
• Variables declared with const cannot be re-assigned so you cannot have the = next to that variable name after declaring it.
• If you see var, it’s from the old version of JavaScript. You can convert it to let (sometimes const if the variable is not re-assigned).

Conditions

Conditions