They keep track of the id of the last checked box and when when another checkbox is checked they use the shiftKey event attribute to see if shift was held while clicking the checkbox. If so they set the checked property of each checkbox in between the two to true.
To determine when a box is checked they probably use an onclick event on the checkboxes
var NUM_BOXES = 10;
// last checkbox the user clicked
var last = -1;
function check(event) {
// in IE, the event object is a property of the window object
// in Mozilla, event object is passed to event handlers as a parameter
if (!event) { event = window.event }
var num = parseInt(/box\[(\d+)\]/.exec(this.name)[1]);
if (event.shiftKey && last != -1) {
var di = num > last ? 1 : -1;
for (var i = last; i != num; i += di) {
document.forms.boxes['box[' + i + ']'].checked = true;
}
}
last = num;
}
function init() {
for (var i = 0; i < NUM_BOXES; i++) {
document.forms.boxes['box[' + i + ']'].onclick = check;
}
}
It seems like every answer I can find online is completely dependent on jQuery for this. JQuery adds very little functionality. Here's a quick version that doesn't require any frameworks:
function allow_group_select_checkboxes(checkbox_wrapper_id){
var lastChecked = null;
var checkboxes = document.querySelectorAll('#'+checkbox_wrapper_id+' input[type="checkbox"]');
//I'm attaching an index attribute because it's easy, but you could do this other ways...
for (var i=0;i<checkboxes.length;i++){
checkboxes[i].setAttribute('data-index',i);
}
for (var i=0;i<checkboxes.length;i++){
checkboxes[i].addEventListener("click",function(e){
if(lastChecked && e.shiftKey) {
var i = parseInt(lastChecked.getAttribute('data-index'));
var j = parseInt(this.getAttribute('data-index'));
var check_or_uncheck = this.checked;
var low = i; var high=j;
if (i>j){
var low = j; var high=i;
}
for(var c=0;c<checkboxes.length;c++){
if (low <= c && c <=high){
checkboxes[c].checked = check_or_uncheck;
}
}
}
lastChecked = this;
});
}
}
And then initialize it whenever you need it:
allow_group_select_checkboxes('[id of a wrapper that contains the checkboxes]')
Inspired by the fine answers provided, here's a plain JavaScript version using Array.prototype to coerce nodelists to use array functions, rather than for loops.
(function () { // encapsulating variables with IIFE
var lastcheck = null // no checkboxes clicked yet
// get desired checkboxes
var checkboxes = document.querySelectorAll('div.itemslist input[type=checkbox]')
// loop over checkboxes to add event listener
Array.prototype.forEach.call(checkboxes, function (cbx, idx) {
cbx.addEventListener('click', function (evt) {
// test for shift key, not first checkbox, and not same checkbox
if ( evt.shiftKey && null !== lastcheck && idx !== lastcheck ) {
// get range of checks between last-checkbox and shift-checkbox
// Math.min/max does our sorting for us
Array.prototype.slice.call(checkboxes, Math.min(lastcheck, idx), Math.max(lastcheck, idx))
// and loop over each
.forEach(function (ccbx) {
ccbx.checked = true
})
}
lastcheck = idx // set this checkbox as last-checked for later
})
})
}())
I took the jQuery version from @BC. and transformed it into an ES6 version, since the code is actually pretty elegantly solving the problem, in case anyone still stumbles across this...
Here is the Elegant implementation. The idea is to store the first selected input to the lastChecked variable and when the user selects the input field with shiftKey we will run a loop and toggle the inBetween(boolean) and mark all the checkboxes with true value.
Inspired by Wesbos.
let checkboxes = document.querySelectorAll('.wrapper input[type="checkbox"]');
let lastChecked;
function logic(e) {
let inBetween = false;
if (e.shiftKey) {
checkboxes.forEach(checkbox => {
if (checkbox === this || checkbox === lastChecked) {
inBetween = !inBetween;
}
if (inBetween) checkbox.checked = true;
})
}
lastChecked = this;
}
checkboxes.forEach((checkbox, i) => checkbox.addEventListener('click', logic));