CODEWITHSUNDEEP
javascript
WolfieeifloW
WolfieeifloW

Reputation: 619

Javascript Get Yesterdays Day of Week

I have a string that contains a day of the week (ex "Monday"). I need to figure out how to take this string and get the previous day of the week.

For example if the string contains "Monday" the new string should output "Sunday".

I feel like there is a simple solution (that isn't 7 IF statements) that I'm missing here.

Upvotes: 7

Views: 211

Answers (5)

Kamil Kiełczewski
Kamil Kiełczewski

Reputation: 92347

Try

let yesterday = {
  'Monday': 'Sunday',
  'Tuesday': 'Monday',
  'Wednesday': 'Tuesday',
  'Thursday': 'Wednesday',
  'Friday': 'Thursday',
  'Saturday': 'Friday',
  'Sunday': 'Saturday',
}

console.log(yesterday['Monday']);

Upvotes: 9

Sergey Mell
Sergey Mell

Reputation: 8040

Your solutions could look as follows

const daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
const index = daysOfWeek.indexOf('Monday');
console.log(index ? daysOfWeek[index - 1] : daysOfWeek[6]);

You just find a position of the current day and take the previous one in the array. The only check you should make for the index === 0 because negative indexes do not return elements from the end of the array in JavaScript

Upvotes: 2

symlink
symlink

Reputation: 12209

You don't need a lot of if statements, just a function that uses array.length and array.indexOf():

let daysOfWeek = ["Monday", "Tuesday", "Wednesday","Thursday","Friday","Saturday","Sunday"];

let yesterday = (today) => {
   if(daysOfWeek.indexOf(today) === 0){
      return daysOfWeek[daysOfWeek.length - 1];
   }else{
      return daysOfWeek[daysOfWeek.indexOf(today) - 1];
   }
}

console.log(yesterday("Sunday"));

Upvotes: 2

Yaniv
Yaniv

Reputation: 829

One straightforward approach, assuming correct input, would be using arrays:

days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
previousDay = days[(days.indexOf(currentDay)-1+7)%7];

Upvotes: 6

mickl
mickl

Reputation: 49945

You can use indexOf and return Sun when you exceed array range:

let currentDay = "Mon";

let days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"];
let prevDay = days[days.indexOf(currentDay) - 1 ] || "Sun";

console.log(prevDay);

Upvotes: 3

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