JS-0239 · Consider using `let` or `const` instead of `var`

Consider using let or const instead of var JS-0239

Anti-pattern

Major

3 months ago — 3 months old

Unexpected var, use let or const instead

174	    window.location.hash = e.target.hash.replace("#", "#" + prefix);
175	})
176	// Read any hash links
177	var hash = document.location.hash;178	if (hash) {
179		$('.nav-tabs a[href="'+hash.replace(prefix,"")+'"]').tab('show');
180	}

Unexpected var, use let or const instead

htdocs/td/dl/dl.js

169	});
170	// https://stackoverflow.com/questions/7862233
171	// Change hash for page-reload
172	var prefix = "tab_";173	$('.nav-tabs.maintabs a').on('shown.bs.tab', function (e) {
174	    window.location.hash = e.target.hash.replace("#", "#" + prefix);
175	})

Unexpected var, use let or const instead

htdocs/td/dl/dl.js

150		
151	});
152	$(".sa").click(function(){
153		var tabtitle = $(this).attr("id").replace("-selectall", "");154		$("#" + tabtitle +"-ui input:enabled[type='checkbox']").prop('checked', true);
155	});
156	$("#missingvalue").change(function(){

Unexpected var, use let or const instead

htdocs/td/dl/dl.js

142
143		var currentdiv = TABS[CURRENTTAB] +"-ui";
144		$("#"+currentdiv).css("display", "block");
145		var btndiv = TABS[CURRENTTAB] +"-btn";146		$("#"+btndiv).removeClass().addClass("btn btn-primary");
147
148		$('#next-btn').prop('disabled', ((CURRENTTAB + 1) == TABS.length));

Unexpected var, use let or const instead

htdocs/td/dl/dl.js

140		$("#"+btndiv).removeClass().addClass("btn btn-default");
141		CURRENTTAB = TABS.indexOf(tabtitle);
142
143		var currentdiv = TABS[CURRENTTAB] +"-ui";144		$("#"+currentdiv).css("display", "block");
145		var btndiv = TABS[CURRENTTAB] +"-btn";
146		$("#"+btndiv).removeClass().addClass("btn btn-primary");

Description

It is recommended to use let or const over var. This will help prevent re-declaration of variables that are in the global scope when using var.

ES6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as this one:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Block scoped variables shadow outer declarations instead of writing to them.

NOTE: There are certain edge cases where users might want to consider var. Consider this example:

var lib = lib || { run: () => {} }

Here, lib might be a library that is exposed to an HTML file using a <script> tag. The var keyword helps avoid re-writing lib if it has already been declared via an injected script that was executed before this one. Ideally, you should let bundlers worry about cases like this. But if you want to use var anyway, consider using a skipcq comment, or disabling the issue altogether.

Bad Practice

var x = "y";
var CONFIG = {};

isudatateam / datateam

Bad Practice

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