Basics Flashcards
What’s exponent operator?
**
What’s the difference between == and ===?
Strict equality (no attempt at type conversion)
What are the three methods for declaring strings?
’ ‘, “ “, ` `
How do you add quotation marks inside a string?
with the \ (escape) character
What are commonly used escape characters in strings?
Code Output \' single quote \" double quote \\ backslash \n newline \r carriage return \t tab \b word boundary \f form feed
What does it mean to say string values are immutable?
They cannot be altered once created, only assigned a new string.
Not allowed: var myStr = "Bob"; myStr[0] = "J";
What is the scope of variables assigned without the var keyword?
global
What happens when a local and global variable have the same name?
the local variable takes precedence
What’s the syntax for a switch statement?
switch(lowercaseLetter) {
case "a":
console.log("A");
break;
case "b":
console.log("B");
break;
}How are case values in a switch statement evaluated?
with strict equality
How do you execute a case in a switch statement if no matching values are found
with default
What does break do in switch statements?
tell javascript to stop executing statements
What’s the syntax for a switch statement that has multiple inputs with the same output?
switch(val) {
case 1:
case 2:
case 3:
result = "1, 2, or 3";
break;What are the two ways to access object properties?
There are two ways to access the properties of an object: dot notation (.) and bracket notation ([])
What’s the syntax for declaring an object?
var myObj = {
prop1: "val1",
prop2: "val2"
};When would you use dot notation to access an objects properties?
When you know the key name and it has no spaces.
What’s the syntax for accessing an object’s values when the key name has spaces?
myObj[“Space Name”]; // Kirk
myObj[‘More Space’]; // Spock
myObj[“NoSpace”]; // USS Enterprise
Note that property names with spaces in them must be in quotes (single or double).
How do you access an object’s values when the key name is a variable?
With bracket notation and no quotes around the variable.
What’s the syntax for deleting an object’s property?
delete ourDog.bark;
What function checks if an object has a property?
.hasOwnProperty(propname)
What’s the syntax for a while loop?
while(i < 5) {
ourArray.push(i);
i++;
}
What’s the difference between a while and do..while loop?
A do…while loop executes the loop body at least once
What’s the syntax for a do…while loop?
do {
ourArray.push(i);
i++;
} while (i < 5);
What does Math.random() do?
generates a random decimal number between 0 (inclusive) and not quite up to 1 (exclusive). Thus Math.random() can return a 0 but never quite return a 1
How do you generate random whole numbers?
Math.floor(Math.random() * 20);
How do you generate random numbers between a maximum and minimum value?
Math.floor(Math.random() * (max - min + 1)) + min
How do you convert a string to an integer?
var a = parseInt(“007”);
How do you convert a string to a number of a different base?
var a = parseInt("11", 2);
The radix variable says that "11" is in the binary system, or base 2. This example converts the string "11" to an integer 3.What’s the syntax for a one line if-else expression?
condition ? expression-if-true : expression-if-false;
What’s the syntax for a multi-line ternary operator?
function findGreaterOrEqual(a, b) {
return (a === b) ? "a and b are equal"
\: (a > b) ? "a is greater"
\: "b is greater";
}What’s the ES6 syntax for declaring functions?
let name = (num1, num2) => {
body
}What does a function without the return keyword return?
undefined
What’s the ES5 syntax for a regular function?
function name(num1, num2) {
body
}What’s the ES5 syntax for an anonymous function?
let name = function(num1, num2) {
body
}What’s the syntax for looping through an object?
for (let key in obj) {
body
}
How do you execute a function on each element of an array?
forEach()
How do you combine all the elements of an array into a single string?
join()
How do you find the index of a single element in an array?
indexOf()
How do you extract a sequential part of an array?
arr.slice([start[, end]])
the resulting array will include the start, but not the end
How do you change the contents of an array by removing or replacing existing elements?
.splice
let arrDeletedItems = arr.splice(start[, deleteCount[, item1[, item2[, …]]]])
What does the splice function return?
the array of deleted elements
How do execute a function on an array and return a new array?
The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.
const map1 = array1.map(x => x * 2);
