Javascript Flashcards
What keyword should you not forget when assigning a variable’s value for the first time?
var
Which logical operator should I use when comparing values and why or why not?
the === or !== is best because it compares the value and the type where as the == or != compares and performs a type conversion
What are considered false values
undefined, null, 0, false, NaN, ‘ ‘ (empty string)
What should you always use to terminate your line?
semi-colon ;
What is an object constructor function?
What does the ‘this’ keyword do?
Javascripts way to create an "object type" or blueprints/classes. An example would be:
function Person(first, last, age, eye) {
this.firstname = first;
this.lastname = last;
this.age = age;
this.eyeColor = eye;
}
The this is the object itself and it 'owns' the code. In other words when a new Person is instantiated, the this will become the new objects.
var myFather = new Person('John', 'Smith', '35', 'blue');what does typeof return?
It returns the datatype
console. log(typeof 42);
output: number
console. log(typeof arr);
output: object
How do you add a new property to an existing object?
myFather.nationality = “Irish”;
How do you add a method to an object?
myFather.name = function () {
return this.firstname + “ “ + this.lastName;
};
this method will be added to myFather only
How do you add a method to a Constructor?
function Person(first, last, age, eye) {
this.firstname = first;
this.lastname = last;
this.age = age;
this.eyeColor = eye;
this.name = function () {
return this.firstname + " " + this.lastName;};
}What are Javascript’s built-in constructors?
var x1 = new Object(); // A new Object object var x2 = new String(); // A new String object var x3 = new Number(); // A new Number object var x4 = new Boolean(); // A new Boolean object var x5 = new Array(); // A new Array object var x6 = new RegExp(); // A new RegExp object var x7 = new Function(); // A new Function object var x8 = new Date(); // A new Date object
What are Javascript literals?
JS primitive values that make writing code faster.
Use object literals {} instead of new Object().
Use string literals "" instead of new String().
Use number literals 12345 instead of new Number().
Use boolean literals true / false instead of new Boolean().
Use array literals [] instead of new Array().
Use pattern literals /()/ instead of new RegExp().
Use function expressions () {} instead of new Function().
What is an anonymous function?
A function that executes automatically when you create it. aka Self-Invoking function. Example:
(function () {
var x = "Hello"; //It will invoke itself without being called
})();How do you get a random item from an array?
var items = [1,2,3,4,5] var randomItem = items[Math.floor(Math.random() * items.length)]
How does the function math.floor() work?
it returns the largest integer less than or equal to a given number
How does the function math.random() work?
it returns a floating-point number in the range of 0-1 (not including 1)
What is return?
when evoked it is a value that is returned to the caller when the function finishes executing
What is a caller?
a caller inserts values (whether it is from the function’s argument or return) between the { } when it executes the function. Once executed, the value is copied in and are available like any other variable.
What is a parameter?
a value that is passed through a function so that the function can behave differently depending on the value that is passed. e.g.:
function greetSomeone(person) {
} person is the paramenter
