Section 1
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What is the difference between != and !== ?
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Mar 1, 2020
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Section 1
(50 cards)
What is the difference between != and !== ?
!= //inequality operator !== //STRICT inequality operator
What is syntax for function names and variables?
camelCase no dashes no periods can't start with a number it CAN start with $ or underscore
compound assignment operators += -= *= /=
Compound assignment operators that (adds or subtracts or multiples or divides) the right-hand operand by the left and stores the result in the left-hand operand; Ex: a += b is equivalent to a = a + b.
what is the format for a switch statement that includes 2 cases and one default?
function guessNum(num) { var answer = " "; switch(num) { case 1: //if the answer == 1 answer = "you got it right!"; break; //all cases end with this case 2: answer = "just missed it"; break; default: //like else: statement answer = "nope"; break; } return answer; }
How do you access 11 and 13 in the following array? var arr = [ [1,2,3], [4,5,6], [7,8,9], [[10,11,12], 13, 14] ];
arr[3][0][1]; // 11 arr[3][1]; //13
What is the syntax for an if statement that evaluates whether myNum is true?
function test (myNum) { if (myNum === 7) { return "It was true"; } return "It was false"; } //notice no semiconlon to close
When do you HAVE to use bracket notation to access an object's properties?
When the property has a space in it's name. EX: myObj["space name"];
multiline comment
/ comment here /
define a variable
Multiple ways: _______________________ var name; name = "Molly"; _____________________________ var name = "Molly"; ______________________________ var name, age; name = "Molly"; age = 5; _______________________ var name = "Molly", quantity = 14;
What does a return do?
It provides a value from a function. Note: nothing that is written after the return statement in the function will execute. Once a you hit the return value, the function is automatically exited
What does the typeof operator do?
determines the type of variable for value. Ex: typeof 7; >number typeof "hello"; >string
Can a function be called before it is declared
Yes. In JavaScript this okay (as long as declared later in script).
How do you set up a for loop?
for (initialization; condition; final expression) { }; ex: var ourArray = [ ]; for (var i = 0; i < 5; i++) { ourArray.push(i); }
single line comment
// comment here
Function Expression
var area = function(width, height) { return width * height; }; //notice semicolon! Different from anonymous function. It cannot be called before you define it!
How do you delete a property of an object?
delete hotel.name;
How do add a new item to the FRONT of an array?
array.unshift()
How do you access the 2nd letter of the following variable: var myStr = "Lindsey";
myStr[1]; *Note bracket notation can just be used here to access character--it CAN'T change the character.
How do you create an array literal?
var colors; colors = ['white', 'red', 'green']; *numbering of arrays starts at 0! Here, 0 is the index and white is its value.
How do you find calculate the number of characters in the variable myStr?
var stringLength = myStr.length;
Return value
When you expect function to provide you with a value. Note: nothing that is written after the return statement in the function will execute.
How do you clear the value of an object's property?
hotel.name = ' ';
How do you link JS script to HTML file
<script type="text/javascript" src="script.js"></script> *generally added at end, before </body> tag
what does -- do in JS?
decrement, subtracts one from current number i--;
How do you call function getArea with the parameters 3 and 5?
getArea(3, 5);
What is the difference between equality operator (==) and strict equality (===) ?
== attempt to convert both values to a common type; === does not Ex: 3 == '3' //true 3 === '3' //false
How do you create an object with constructor notation?
var hotel = new Object(); hotel.name = 'Quay'; hotel.checkAvailability = function() { return this.rooms - this.booked; }; *note name is the key and Quay is the value.
How do you change the third item in the array named colors?
colors[2] = 'beige';
How do you alter the name property of the object dog with both bracket and dot notation?
dog["name"] = "Rudy"; dog.name = "Rudy;
What is an Immediately Invoked Function Expression (IIFE)
Not given a name. They are involved as soon as interpreter reaches them. Ex: var area = (function() { var width = 3; var height = 2; return width * height; } () ); *parens near end tell interpreter to run immediately. Any variables in anon. functin won't conflict with variables with same name in script.
What are global variables?
They are created outside a function. They can be used anywhere. (Note* they use more memory and can make scripts slower).
What method do you use to check if an object has a certain property?
.hasOwnProperty(propname); Ex: dog.hasOwnProperty("name"); //note strings on name--even with dot notation!
How do you push "green" onto the array colors?
colors.push("green"); //adds green to end of array
How do add the property sound to the object dog using both bracket and dot notation?
dog.sound = "woof"; dog["sound"] = "woof"; //note string for bracket notation
How do you access the length of the array named colors?
colors.length;
Can a function be called before it is declared
Yes. In JavaScript this okay (as long as variable is declared later in script).
What is the syntax for a multi-dimensional array to hold the names of NBA players separated by team?
var NBAplayers = [["Laker1", "Laker2"], ["Celtic1", "Celtic2"]];
How do you remove the FIRST element from an array?
array.shift(); //takes no argument, just empty parens
How do you find the last index of an array with an unknown amount of items?
myArray.length -1
How do you remove the last element from the following: colors = ["red", "blue", "green"];
colors.pop(); //pop always removes the last element of an array
what does || do?
logical or operator. It returns true if either of the operands are true. if (num < 5 || num > 10) { return "Yes": }
How do you change the third item in the array named colors?
colors[2] = 'beige';
what is the syntax for the object dog with the properties name and legs?
var dog = { name: "Kaya", legs: 4 }; NOTE: commas used to separate properties and semicolon used at end of object
How do you access an object (using dot notation)?
var hotelName = hotel.name; (or you can use square brackets, but NOT to access methods) var hotelName = hotel['name'];
what does && do?
logical and operator: returns true if and only if the operands to the left and right of operator are true. Ex: if (num > 5 && num < 10) { return "Yes": }
what is the order of if/else if/ and else conditions?
if else if else if else (only final statement)
How do you delete the property sound from the object dog using both dot and bracket notation?
delete dog.sound; delete dog["sound"];
What is an Immediately Invoked Function Expression (IIFE)
Not given a name. They are involved as soon as interpreter reaches them. Ex: var area = (function() { var width = 3; var height = 2; return width * height; } () ); *parens near end tell interpreter to run immediately. Any variables in anon. function won't conflict with variables with same name in script.
--
decrement, subtracts from from current number i--;
How do you create an array literal?
var colors = ['white', 'red', 'green']; *numbering of arrays starts at 0! Here, 0 is the index and white is its value.
Section 2
(16 cards)