The project I was working on today involved front-end Javascript. To summarize the issue and solution, I needed to add click handlers to links on a page that redirect users to other pages. I utilized two JavaScript arrays: arrayOfRedirectLinks and pageLinkElements:
var arrayOfRedirectLinks, pageLinkElements;
Initially, I wrote the addEventHandlers function as follows:
var addEventHandlers = function() {
var i, link;
for( var i in arrayOfRedirectLinks) {
link = arrayOfRedirectLinks[i];
pageLinkElements[i].addEventListener('click', function(e) {
e.preventDefault();
window.location = link;
});
}
}
However, upon testing this solution, I found that all links redirected me to the same destination (the last link in arrayOfRedirectLinks).
Eventually, I came across a similar problem and solution described here: Javascript multiple dynamic addEventListener created in for loop - passing parameters not working
The following revised solutions resolved my issue:
var addEventHandlers = function() {
var i, link;
for( var i in arrayOfRedirectLinks) {
(function(link){
link = arrayOfRedirectLinks[i];
pageLinkElements[i].addEventListener('click', function(e) {
e.preventDefault();
window.location = link;
});
}(link));
}
}
and
var passLink = function(link) {
return function(e) {
e.preventDefault();
window.location = link;
};
};
var addEventHandlers = function() {
var i, link;
for( var i in arrayOfRedirectLinks) {
link = arrayOfRedirectLinks[i];
pageLinkElements[i].addEventListener('click',passLink(link));
}
}
This updated approach solved the issue, though the exact reasoning behind its success remains unclear to me. My explanation is as follows:
Functions in JavaScript reference variables from the scope they were declared in. This means my event handler obtains a reference to the
linkvariable within theaddEventHandlersfunction.Due to the referenced nature of the
linkvariable, any updates made to it will affect all click handlers linked to it. This resulted in all links directing to the last value oflinkin the arrayarrayOfRedirectLinks.Passing the
linkvariable as a parameter to another function creates a new scope where thelinkshares only its initial value with the passed parameter. Consequently, each event handler'slinkis isolated, maintaining the correct value fromarrayOfRedirectLinks[i].In conclusion, passing the
linkto the click handler creates distinct references for each instance, preventing interference between them and preserving the correct redirection values.
Does this explanation accurately depict the situation?