Splice and Slice both are Javascript Array functions.

Splice vs Slice

1. The splice() method returns the removed item(s) in an array and slice() method returns the selected element(s) in an array, as a new array object.

2. The splice() method changes the original array and slice() method doesn’t change the original array.

3. The splice() method can take n number of arguments and slice() method takes 2 arguments.

Splice with Example

Argument 1: Index, Required. An integer that specifies at what position to add /remove items, Use negative values to specify the position from the end of the array.

Argument 2: Optional. The number of items to be removed. If set to 0(zero), no items will be removed. And if not passed, all item(s) from provided index will be removed.

Argument 3…n: Optional. The new item(s) to be added to the array.

var array=[1,2,3,4,5];
console.log(array.splice(2));
// shows [3, 4, 5], returned removed item(s) as a new array object.
 
console.log(array);
// shows [1, 2], original array altered.
 
var array2=[6,7,8,9,0];
console.log(array2.splice(2,1));
// shows [8]
 
console.log(array2.splice(2,0));
//shows [] , as no item(s) removed.
 
console.log(array2);
// shows [6,7,9,0]

Slice with Example

Argument 1: Required. An integer that specifies where to start the selection (The first element has an index of 0). Use negative numbers to select from the end of an array.

Argument 2: Optional. An integer that specifies where to end the selection but does not include. If omitted, all elements from the start position and to the end of the array will be selected. Use negative numbers to select from the end of an array.

var array=[1,2,3,4,5]
console.log(array.slice(2));
// shows [3, 4, 5], returned selected element(s).
 
console.log(array.slice(-2));
// shows [4, 5], returned selected element(s).
console.log(array);
// shows [1, 2, 3, 4, 5], original array remains intact.
 
var array2=[6,7,8,9,0];
console.log(array2.slice(2,4));
// shows [8, 9]
 
console.log(array2.slice(-2,4));
// shows [9]
 
console.log(array2.slice(-3,-1));
// shows [8, 9]
 
console.log(array2);
// shows [6, 7, 8, 9, 0]

Check out Array.prototype.slice().

When you call array.slice(), that's returning a slice of your array (as another array).

var array = ['zero', 'one', 'two', 'three'];
// Grab the elements from `array`
// beginning at 1 and up to (not including) 3.
var sliced = array.slice(1, 3);

console.log(array);    // ['zero', 'one', 'two', 'three']
console.log(sliced);   // ['one', 'two']
console.log(sliced[0]) // 'one'

In your code, you are executing array.slice(-1). The documentation says that "[a] negative index can be used, indicating an offset from the end of the sequence. slice(-2) extracts the last two elements in the sequence." Thus, your array.slice(-1) is returning a new array populated with the last element of your original, array.

var array = ['zero', 'one', 'two', 'three'];
var sliced = array.slice(-1);

console.log(array);      // ['zero', 'one', 'two', 'three']
console.log(sliced);     // ['three']
console.log(sliced[0]);  // 'three'

// All together, it looks like this. 
// I'm using `alert()` instead of `console.log()` 
// to mirror your code.

alert(array.slice(-1)[0]); // 'three'

Why do you need the strings to not have quotes? Is there an specific reason?

In js you need to put quotes on strings. If you try for example declaring an array in the way you did above the following will happen:

let x = [janaina,joao,julia]

VM203:1 Uncaught ReferenceError: janaina is not defined at :1:10

So, correct way to delcare your array:

let x = ['janaina','joao','julia']

Now slice will work:

x.slice(0,1);

The result will be:

['janaina']