It's unnecessary to concatenate two strings together, such as:
var foo = "a" + "b";
This code is likely the result of refactoring where a variable was removed from the concatenation (such as
"a" + b + "b"). In such a case, the concatenation isn't important and the code can be rewritten as:
var foo = "ab";
This rule aims to flag the concatenation of 2 literals when they could be combined into a single literal. Literals can be strings or template literals.
Examples of incorrect code for this rule:
/*eslint no-useless-concat: "error"*/ /*eslint-env es6*/ var a = `some` + `string`; // these are the same as "10" var a = '1' + '0'; var a = '1' + `0`; var a = `1` + '0'; var a = `1` + `0`;
Examples of correct code for this rule:
/*eslint no-useless-concat: "error"*/ // when a non string is included var c = a + b; var c = '1' + a; var a = 1 + '1'; var c = 1 - 2; // when the string concatenation is multiline var c = "foo" + "bar";
If you don't want to be notified about unnecessary string concatenation, you can safely disable this rule.
This rule was introduced in ESLint 1.3.0.
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