Strings and arrays

Question 1

Turn ‘apples, bananas, oranges, pears and salsa’ into an array but without ‘and salsa’

Answer 1

theString.split( ‘ ‘, 4);

Question 2

What does someString.split(“”) do (first arg is empty string)?

Answer 2

Converts string to an array of characters. “abc” becomes [‘a’,’b’,’c’];

Question 3

var arr = ["apple", "orange", "grape"]; 
var c = arr.push("banana"); 
what is c?

Answer 3

It returns the number 4 because push returns the length of the array, not the array.

Question 4

var a = [a,b,c,d,e]. What does b = a.splice() do?

Answer 4

a will become an empty array and b will become [a,b,c,d,e]

Question 5

someArray.splice(arg1, arg2); What is arg1 and arg2?

Answer 5

arg1 is the index to remove from; arg 2 is how many items after that.

Question 6

How would you change [1,0,0,0,5] to [1, 2, 3, 4,5] using an array method?

Answer 6

theArray.splice( 1, 3, 2, 3 ,4);

Question 7

What’s the best way to copy array myArr into newArr?

Answer 7

newArr = myArr.slice( ) or slice( 0 );

Question 8

var a = "My String"; 
var b = a.slice(1); 
What happens to a and to b?

Answer 8

a = 'My String'
b = 'y String'

Question 9

How are substr(), substring(), and slice() similar/different?

Answer 9

The first arg in all is the starting index.
For substring and slice, arg2 is ending index.
For substr it’s the total characters/elements to take including starting index;

Question 10

arr1 = [ 0, 2, 4];
arr2 = [ 1, 3, 5];
How could I change arr1 to be 0,2,4,1,3,5 ?

Answer 10

arr1 = arr1.concat(arr2); // concat is non-destructive.

Question 11

what are the location methods?

Answer 11

indexof(arrayOrString, [startIndex]); // counts forward from startindex
lastIndexOf(arrayOrString, [startindex]); // counts back from startindex

Question 12

What does the array sort function’s compare function return?

Answer 12

-1, 0, or 1 depending on whether a<b>b</b>

Question 13

Turn [“Tom”, “Bill”, “Jerry”] into the string “Tom, Bill, Jerry”?

Answer 13

Use array.join(“, “);

Question 14

Name two ways to find the 4th character in a string, “cats”

Answer 14

“cats”.charAt(3);

“cats”[3];

Question 15

shift vs unshift?

Answer 15

myArray.shift() will remove the first item from an array and return it. Unshift(“val”) adds a value to start of array and returns new length.

Question 16

When handling strings, what’s a handy function for dealing with white space?

Answer 16

trim(). Use this when doing things like str.split();

Question 17

What are the five iterative methods for arrays?

Answer 17

every(); some(); filter(); forEach(); map();

Question 18

When passing a function to an iterative array, what are the parameters you can include?

Answer 18

item, index, and array — the ‘array’ argument is the array being acted on.

Question 19

var arr = [1,2,3,4,5,6,7,8];
how could you create an array that had only the even values in arr?

Answer 19

var evenVals = arr.filter(function(item, index, array){ return item%2==0; });

Question 20

var arr = [1,2,3,4,5,6,7,8];
how could you create an array which was the same as arr except every value was doubled?

Answer 20

var doubledArr = arr.map(function(item, index, array){ return item * 2; });

Question 21

var arr = [1,2,3,4,5,6,7,8];
What if you wanted to know if every item in this array was positive?

Answer 21

var allPositive = arr.every(function(item, index, array){ return item > 0; });

Question 22

How is array.filter() different from array.map()?

Answer 22

For each item, it evaluates an expression. It only returns that item if the expression is true. It doesn’t alter the item. Array.map() can return anything whether true or false.

Question 23

What is a concise and popular way to convert an array-like object to an actual array?

Answer 23

newArr = Array.prototype.slice.call( someNodeList ) or
newArr = [].slice.call( jqueryObj );

Question 24

What arguments does the myArray.reduce() function take and what does it do?

Answer 24

The reduce function takes two arguments, a function and a startingValue. The function takes (accumulator, currentValue, index, array) and returns a value. The startingValue can be anything.

Question 25

What are two ways to find if an array contains a particular value?

Answer 25

someArray.indexOf(myValue) > -1; // yes!

someArray.includes(myValue) === true; // yes!