Get the first and last item in an Array - JS

问题:

I am trying to get the first and last item in array and display them in an object.

What i did is that I use the first and last function and then assign the first item as the key and the last item as the value.

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

function firstAndLast(array) {

var firstItem = myArray.first;
var lastItem = myArray.last;

 var objOutput = {
   firstItem : lastItem 
  };

}

var display = transformFirstAndLast(myArray);

console.log(display);

however this one gets me into trouble. It says undefined. Any idea why is that?

回答1:

I've modified your code :

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

function firstAndLast(array) {

var firstItem = myArray[0];
var lastItem = myArray[myArray.length-1];

 var objOutput = {
   first : firstItem,
   last : lastItem
  };

return objOutput;
}

var display = firstAndLast(myArray);

console.log(display);

UPDATE: New Modification

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

function firstAndLast(array) {

var firstItem = myArray[0];
var lastItem = myArray[myArray.length-1];

var objOutput = {};
objOutput[firstItem]=lastItem

return objOutput;
}

var display = firstAndLast(myArray);

console.log(display);

回答2:

ES6

var objOutput = { [myArray[0]]: [...myArray].pop() }

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

var objOutput = { [myArray[0]]: [...myArray].pop() }

console.log(objOutput);

回答3:

With ES6 and destructuring:

const myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

const { 0: first, length, [length -1]: last } = myArray //getting first and last el from array
const obj = { first, last }

console.log(obj) // {  first: "Rodel",  last: "Betus" }

回答4:

To make your first and last properties work as you want, define them as properties with "getters" on the array prototype.

(You also have an inconsistency between firstAndLastArray and transformFirstAndLast, which needed to be fixed.)

Returning {firstName: lastName} will not do what you presumably want, since it will yield the key firstName. To use the actual first name as the key, use computed property names ({[firstName]: lastName}).

Object.defineProperties(Array.prototype, {
  first: { get() { return this[0]; }},
  last:  { get() { return this[this.length - 1]; }}
});

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

function firstAndLast(array) {
  var firstItem = myArray.first;
  var lastItem = myArray.last;
  
  return {[firstItem]: lastItem};
}

var display = firstAndLast(myArray);

console.log(display);

Or, much more simply, just

function firstAndLast(array) {
  return {[array[0]]: array[array.length - 1]};
}

If you don't want to, or cannot, use computed property names, then

function firstAndLast(array) {
  var result = {};
  result[array[0]] = array[array.length - 1];
  return result;
}

回答5:

Do like this :-

var myArray = ['Rodel', 'Mike', 'Ronnie', 'Betus'];

function firstAndLast(myArr) {

    var firstItem = myArr[0];
    var lastItem = myArr[myArr.length - 1];
    var objOutput = {}; 
    objOutput[firstItem] = lastItem;
    return objOutput;
}

var display = firstAndLast(myArray);

console.log(display);

回答6:

well, I have another idea... for ex.:

const all = ['food', 'clean', 'cat', 'shower', 'work out']
console.log(`you have ${all.length} all!`)
console.log(`Todo: ${all[0]}`)
console.log(`Todo: ${all[all.length - 1]}`)