Flash cards
Review the key moves
What is the main idea behind JavaScript 2009 (ES5)?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ str = "HELLO WORLD";Put the learning moves in the order that makes the concept easiest to apply.
ECMAScript 2009
The first major revision to JavaScript .
ECMAScript 2009 is also known as ES5.
ES5 Features
| Feature | Description |
|---|---|
| "use strict" | Allows code to be executed in "strict mode" |
| String [] access | Returns the character at a specified index in a string |
| Multiline strings | Aallows strings over multiple lines if escaped with \ |
| String.trim() | Removes whitespace from both sides of a string |
| Array.isArray() | Returns true if a variable is an array |
| Array forEach() | Calls a function for each array element |
| Array map() | Creates a new array from a function on each element |
| Array filter() | Creates an array from array elements that passes a test |
| Array reduce() | Reduces an array to a single value (from left) |
| Array reduceRight() | Reduces an array to a single value (from right) |
| Array every() | Checks if all array values pass a test |
| Array some() | Checks if some values pass a test |
| Array indexOf() | Search for an element value and returns its position |
| Array lastIndexOf() | Search for an element value and returns its position |
| JSON.parse() | Convert JSON into a JavaScript object |
| JSON.stringify() | Convert JSON into a string |
| Date.now() | Returns the number of milliseconds since zero date |
| Date toISOString() | Converts a date object into to an ISO string |
| Date toJSON() | Converts a date object into to a JSON string |
| Property getters | Allows for defining how a property value is retrieved |
| Property setters | Allows for defining how a property value is set |
| Reserved names | Allows reserved names as property names |
| Object.create() | Creates an object from an existing object |
| Object.keys() | Returns an array with the keys of an object |
| Object management | Object management methods |
| Object protection | Object protection methods |
| Object defineProperty() | Allows for defining or changing object properties |
| Function bind() | Let objects borrow methods from other objects |
| Trailing commas | allows trailing commas in object and array definitions: |
Browser Support
JavaScript 2009 is supported in all modern browsers since July 2013 :
| Chrome 23 | IE/Edge 10 | Firefox 21 | Safari 6 | Opera 15 |
|---|---|---|---|---|
| Sep 2012 | Sep 2012 | Apr 2013 | Jul 2012 | Jul 2013 |
The "use strict" Directive
"use strict" defines that the JavaScript code should be executed in "strict mode".
With strict mode you can, for example, not use undeclared variables.
You can use strict mode in all your programs. It helps you to write cleaner code, like preventing you from using undeclared variables.
"use strict" is just a string expression. Old browsers will not throw an error if they don't understand it.
Property Access on Strings
The charAt() method returns the character at a specified index (position) in a string:
Example
let str = "HELLO WORLD";
str.charAt(0); // returns HExample
let str = "HELLO WORLD";
str[0]; // returns HES5 allows property access on strings
Property access on string might be a little unpredictable.
Read more in JS String Methods .
Strings Over Multiple Lines
"Hello \ Dolly!";The \ method might not have universal support. Older browsers might treat the spaces around the backslash differently. Some older browsers do not allow spaces behind the \ character.
A safer way to break up a string literal, is to use string addition:
"Hello " + "Dolly!";Reserved Words as Property Names
ES5 allows reserved words as property names:
Object Example
var obj = {name: "John", new: "yes"}String trim()
The trim() method removes whitespace from both sides of a string.
Example
var str = " Hello World! ";
alert(str.trim());Learn more in JS String Methods .
Array.isArray()
The isArray() method checks whether an object is an array.
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
result = Array.isArray(fruits);Learn more in JS Array Methods .
Array forEach()
The forEach() method calls a function once for each array element.
Example
const numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);Learn more in JS Array Iteration Methods .
Array map()
The map() method creates a new array by performing a function on each array element.
Example
const numbers1 = [45, 4, 9, 16, 25];
const numbers2 = numbers1.map(myFunction);
function myFunction(value) {
return value * 2;
}Learn more in JS Array Iteration Methods .
Array filter()
The filter() method creates a new array from array elements that passes a test.
Example
const numbers = [45, 4, 9, 16, 25];
const over18 = numbers.filter(myFunction);
function myFunction(value) {
return value > 18;
}Learn more in JS Array Iteration Methods .
Array reduce()
The reduce() method reduces an array to a single value.
Example
const numbers = [45, 4, 9, 16, 25];
let sum = numbers.reduce(myFunction);
function myFunction(total, value) {
return total + value;
}Learn more in JS Array Iteration Methods .
Array reduceRight()
The reduceRight() method reduces an array to a single value (from right to left).
Example
const numbers1 = [45, 4, 9, 16, 25];
let sum = numbers1.reduceRight(myFunction);
function myFunction(total, value) {
return total + value;
}Learn more in JS Array Iteration Methods .
Array every()
The every() method checks if all array values pass a test.
Example
const numbers = [45, 4, 9, 16, 25];
let allOver18 = numbers.every(myFunction);
function myFunction(value) {
return value > 18;
}Learn more in JS Array Iteration Methods .
Array some()
The some() method checks if some array values pass a test.
Example
const numbers = [45, 4, 9, 16, 25];
let allOver18 = numbers.some(myFunction);
function myFunction(value) {
return value > 18;
}Learn more in JS Array Iteration Methods .
Array indexOf()
The indexOf() method searches for an element value and returns its position.
Example
const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.indexOf("Apple") + 1;Learn more in JS Array Search Methods .
Array lastIndexOf()
lastIndexOf() is the same as indexOf() , but searches from the end of the array.
Example
const fruits = ["Apple", "Orange", "Apple", "Mango"];
let position = fruits.lastIndexOf("Apple") + 1;Learn more in JS Array Search Methods .
JSON.parse()
A common use of JSON is to receive data from a web server.
Imagine you received this text string from a web server:
'{"name":"John", "age":30, "city":"New York"}'The JavaScript function JSON.parse() is used to convert the text into a JavaScript object:
Example
const txt = '{"name":"John", "age":30, "city":"New York"}'
const myObj = JSON.parse(txt);Read more in our JSON Tutorial .
JSON.stringify()
A common use of JSON is to send data to a web server.
When sending data to a web server, the data has to be a string.
Imagine we have this object in JavaScript:
const myObj = {name:"John", age:30, city:"New York"};Use the JavaScript function JSON.stringify() to convert it into a string.
const myJSON = JSON.stringify(myObj);The result will be a string following the JSON notation.
myJSON is now a string, and ready to be sent to a server:
Example
const myObj = {name:"John", age:30, city:"New York"};
const myJSON = JSON.stringify(myObj);Read more in our JSON Tutorial .
Date.now()
Date.now() returns the number of milliseconds since zero date (January 1. 1970 00:00:00 UTC).
Example
var timInMSs = Date.now();Date.now() returns the same as getTime() performed on a Date object.
Learn more in JS Date Methods .
Date toISOString()
The toISOString() method converts a Date object to a string, using the ISO standard format:
Example
const d = new Date();
document.getElementById("demo").innerHTML = d.toISOString();Learn more in JS Date Methods .
Date toJSON()
toJSON() converts a Date object into a string, formatted as a JSON date.
JSON dates have the same format as the ISO-8601 standard: YYYY-MM-DDTHH:mm:ss.sssZ:
Example
d = new Date();
document.getElementById("demo").innerHTML = d.toJSON();Learn more in JS Date Methods .
Property Getters
A property getter is a method that allows you to define how a property value is retrieved when it is accessed.
This example creates a getter for a property called fullName:
Example
// Create an object: const Person = { firstName: "John", lastName : "Doe", get fullName() {
return this.firstName + " " + this.lastName;
}
};
// Display data from the object using a getter: document.getElementById("demo").innerHTML = Person.fullName;Learn more about Gettes and Setters in JS Object Accessors