Author: shahprashant

ES6 / ES2015 Additions

Arrow functions (or fat functions)?Arrow functions (or fat functions)

An arrow function expression is a syntactically compact alternative to a regular function expression, although without its own bindings to the this, arguments, super, or new.target keywords. Arrow function expressions are ill suited as methods, and they cannot be used as constructors.

The key difference, despite being shorter to write, is that arrow functions do not create their own value for ‘this’.


If the function body contains just a single statement, you can omit the brackets and write all on a single line:

const myFunction = () => doSomething()

https://flaviocopes.com/javascript-arrow-functions/

(parameters) => { statements }

Arrow functions and Lexical this

https://hackernoon.com/javascript-es6-arrow-functions-and-lexical-this-f2a3e2a5e8c4

Template Strings / Template Literals


https://wesbos.com/javascript-template-strings/

Object Destructuring

https://dev.to/sarah_chima/object-destructuring-in-es6-3fm

Adding to Array

[…oldArray, itemToAdd]

A simple todo app in javascript

Asked in Box onsite interview. With a node.js server on backend. 

$().ready(function() {
   $('#add').on('click', addTask);
   $('#tasks').on('click', markComplete);
   // Alternative way
   // var tasksElement = document.getElementById('tasks');
   // tasksElement.addEventListener('click', markComplete);
   //document.getElementById('task-input').onkeydown = function(e){
   $('#task-input').on('keydown', function(e) {
       if(e && e.keyCode == 13){
            addTask();
       }
   });

   function renderTask(result) {
        var checkboxContainerId = 'check' + result.id;
        var taskTextId = 'tasktext-' + result.id;
        if (result.done == '1') {
            checkedState = ' checked ';
        } else {
            checkedState = '';
        }
        taskHtml = '
  • ';
        taskHtml += '';
        taskHtml += '' + result.data + '
    • ';
        $('#tasks').append(taskHtml);
   }

   function taskAdded(result) {
        renderTask(result);
        $('#task-input').val('');
   }

   function renderResults(results) {
        results.forEach(renderTask);
   }

   function addTask(e) {
       url = 'http://localhost:9898/todo/tasks/create';
       inputData = $('#task-input').val();

       if (!inputData) {
           return;
       }
       $.ajax({
           url: url,
           type: "POST",
           data: {data: inputData} ,
           success: taskAdded,
       });
    }

    function markComplete(e) {
        var done;
        if (e.target && e.target.matches("input.task-checkbox")) {
            var taskId = $(e.target).attr('task-id');
            if ($(e.target).is(":checked")) {
                done = "1";
            } else {
                done = "-1";
            }
            var editUrl = 'http://localhost:9898/todo/tasks/' + taskId + '/edit';
            $.ajax({
               url: editUrl,
               type: "POST",
               data: {done: done},
               success: function(result) {
               }
            });
        }
    }

    var getTasksUrl = 'http://localhost:9898/todo/tasks';
    $.ajax({
       url: getTasksUrl,
       type: "GET",
       success: renderResults,
    });
}
);

    Atlassian Hackerrank Interview

    1) Implement a method ‘find’ that will find the starting index (zero based) where the second list occurs as a sub-list in the first list. It should return -1 if the sub-list cannot be found. Arguments are always given, not empty.

    Combinations of a String

    Implement a function that prints all possible combinations of a string.

    A string “12” is the same as string “21”.

    Note : The below function will work for unique strings like “wxyz” but not for “aabc”.  One quick to fix it for “aabc” would be to store the output strings in a hash and then output the hash.

    Check this video for good explanation of “AABC” :

    function combine($instr, $outstr, $index)
{
    for ($i = $index; $i < strlen($instr); $i++)
    {

        $outstr = $outstr . $instr[$i];
        echo "$outstr\n";
        combine($instr, $outstr, $i + 1);
        $outstr = substr($outstr, 0, -1);
    }
}

combine("wxyz", "", 0);