what js? itself
TRANSCRIPT
What JavaScript?Remove your whats
of JavaScript
The Creation
Brendan Eich
Made JavaScript in 10 days.Hence..
JavaScript
Simple to use.
It really doesn’t care
Semicolons are optional
Parameters may or may not be passed
It really doesn’t carefunction getMessage(message) {
internalVariable = “The message is: ”
return internalVariable + message
}
var result = getMessage(“dogs are nice”, 123, undefined, “etc”)
console.log( result )// this’d positively print “The message is: dogs are nice” without errors
It really doesn’t care
Order of execution isn’t the order written
It really doesn’t caredoSomething()
function doSomething() {
console.log( ‘doing something’ )
}
// This do works..
Weakly typed
All variables may contain anything.
var something = 5;
console.log(something); // shows a 5
function sayHi() { return “Hi!”;}
something = sayHi();
console.log(something); // shows hi!
Weakly typed
Weakly typed
Operations between types can be executed
Conversion on the fly will occur
Weakly typedvar firstValue = 0;
firstValue++; // increase the integer
console.log(firstValue); // shows 1
firstValue += “1”; // concatenates 1 with “1”
console.log(firstValue); // shows “11”
Discovering JS
Types
Conditionals
Types Conversion
Scope
Types
Undefined
Null
Boolean
String
Number
Object including Array
Type undefined
People say that undefined may change the value. I don’t care about that.
if (newVariable === undefined)
This is perfectly fine for my standards.
(function(undefined) {
console.log(undefined); // Prints the given string, my own undefined
})(“my own undefined”);
This is stupid. So I don’t care about undefined not being undefined.
Type null
Very common value in other languages.
Can be seen a lot retrieving data from APIs.
var received = null;
if (received === null) {} // True
if (!received) {} // True too
Type boolean
var that = true;
if (that === true) {} // This is silly
if (that) {} // This is better
if (that == false) {} // Same as the first, silly
if (!that) {} // This is great
Type string
var text = “There was a time”;
if (text != “”)
console.log(“Text is not empty”);
// Above code is far too silly, it can be simpler as below
if (text)
console.log(“Text is not empty”);
Type number
var luckNumber = 5;
if (luckNumber != 0)
console.log(“Number is not zero”);
// This can be easier:
if (luckNumber)
console.log(“Number is positive or negative, not zero”);
Type object
// Right way to initialize an object, not using new
var virtualObject = {};
if (virtualObject)
console.log(“Object exist”); // Even without attributes, it exist
virtualObject.firstAttribute = 1234; // Add attribute
if (virtualObject.unexistingMethod) // Continue only if method available
virtualObject.unexistingMethod(); // Unknown method error prevented
Type object
var dogs = [];
if (dogs) // Object actually exist
dogs.push(“Terry”); // Now has one element
console.log(dogs); // Prints [“Terry”]
If (dogs.length) // Length won’t be zero
console.log(“Array has elements”); // So this actually prints
Discovering JS
Types
Conditionals
Types Conversion
Scope
Conditionals
With or without brackets conditionals must be understood.
Conditionals
if (typeof aName == “string” && aName != “”) {
console.log(“Say hello to ” + aName);
}
This is wrong, javascript has a conditional of 3 equals.
Do NEVER use the 2 equals.
2 sometimes are OK, 3 will be always OK. Use 3 equals always.
Conditionals
if (typeof aName === “string” && aName !== “”) {
console.log(“Say hello to ” + aName);
}
Now this is still pretty awful. If aName is integer 18 then you cannot print hello to 18.
Conditionals
if (aName !== “”) {
console.log(“Say hello to ” + aName);
}
Yet horrible, there is no need to ask for not empty string explicitly when it can be simpler.
Conditionals
// From `if (typeof aName == “string” && aName != “”)`
// To
if (aName) {
console.log(“Say hello to ” + aName);
}
Simplicity is on our side. Take that [INSERT CORRECT STARS WAR CHARACTER]!
Conditionals
ALWAYS USE 3 EQUALS
Types Conversion
Now we are entering to the fun side
JavaScript is well known for its types conversion table
Also for its logic tables
And for everything else, but not in the good way
More as a joke
So lets try to get a good laugh from it
Types conversion
“”+1234
Types conversion
“1234”
Types conversion
+“1.357”
Types conversion
1.357
Types conversion
!!“gaga”
Types conversion
true
Types conversion
!!0
Types conversion
false
Types conversion
!!undefined
Types conversion
false
Types conversion
!!dogs.length
Types conversion
false/true
Discovering JS
Types
Conditionals
Types Conversion
Scope
Scope
We can define a scope as a set of rules for storing variables in some location, and for finding those variables at a later time.
Scope
Nested Scopes
JavaScripts starts at the currently executing scope, looks for the variable there, then if not found, keeps going up one level, and so on. If the outermost global scope is reached, the search stops, whether it finds the variable or not.
Nested Scopes
