README.md

Section 06: The every and some Helper

• The every and some Helper
• every() and some() in Practice
• [Exercise] Finding Submitted Users
• [Exercise] In Progress Network Requests

The every and some Helper

The every() and some() helper will checks the elements in an array pass the provided function or not.

• The every() method checks if all elements in an array pass a test (provided as a function).
• The some() method checks if any of the elements in an array pass a test (provided as a function).

The every() method executes the provided function once for each array element and returns the value of the first element passing the test by provided function. Otherwise it returns undefined.

let computers = [
  { name: 'Apple', ram: 24 },
  { name: 'Compaq', ram: 4 },
  { name: 'Acer', ram: 32}
];

// loop the array by using for loop
let allComputersCanRunProgram = true;
let onlySomeComputersCanRunProgram = false;

for (let i = 0; i < computers.length; i++) {
  let computer = computers[i];

  if (computer.ram < 16) {
    allComputersCanRunProgram = false;
  } else {
    onlySomeComputersCanRunProgram = true;
  }
}

// loop the array by using every() and some() method
let allComputersCanRunProgram = computers.every(computer => computer.ram > 16);
let onlySomeComputersCanRunProgram = computers.some(computer => computer.ram > 16);

Note that the every() and some() methods don't change the original array. Moreover, the some() method will return and doesn't check remaining element whenever there is an element in that array pass the test.

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every() and some() in Practice

We would use every() or some() method to create the criteria for if-statement in practice.

class Field(value) {
  constructor(value) {
    this.value = value;
  }

  validate() {
    return this.value.length > 0;
  }
}

let username = new Field("2cool");
let password = new Field("my_password");
let birthdate = new Field("10/10/2010");

let fields = [username, password, birthdate];
let formIsValid = fields.every(field => return field.validate());

if (formIsValid) {
  // allow user to submit!
} else {
  // show an error message.
}

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[Exercise] Finding Submitted Users

Question

Given an array of users, return true if every user has submitted a request form. Assign the result to the variable hasSumbmitted.

var users = [
  { id: 21, hasSubmitted: true },
  { id: 62, hasSubmitted: false },
  { id: 4, hasSubmitted: true }
];

var hasSubmitted;

Solution

let users = [
  { id: 21, hasSubmitted: true },
  { id: 62, hasSubmitted: false },
  { id: 4, hasSubmitted: true }
];

let hasSubmitted = users.every(user => user.hasSubmitted);

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[Exercise] In Progress Network Requests

Question

Given an array of network objects representing network requests, assign the boolean true to the variable inProgress if any network request has a status of pending.

var requests = [
  { url: '/photos', status: 'complete' },
  { url: '/albums', status: 'pending' },
  { url: '/users', status: 'failed' }
];

var inProgress;

Solution

let requests = [
  { url: '/photos', status: 'complete' },
  { url: '/albums', status: 'pending' },
  { url: '/users', status: 'failed' }
];

let inProgress = requests.some(request => request.status === 'pending');

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