Enforces return statements in callbacks of array's methods (array-callback-return)
Array
has several methods for filtering, mapping, and folding. If we forget to write return
statement in a callback of those, it's probably a mistake.
// example: convert ['a', 'b', 'c'] --> {a: 0, b: 1, c: 2}
var indexMap = myArray.reduce(function(memo, item, index) {
memo[item] = index;
}, {}); // Error: cannot set property 'b' of undefined
This rule enforces usage of return
statement in callbacks of array's methods.
Rule Details
This rule finds callback functions of the following methods, then checks usage of return
statement.
Array.from
Array.prototype.every
Array.prototype.filter
Array.prototype.find
Array.prototype.findIndex
Array.prototype.map
Array.prototype.reduce
Array.prototype.reduceRight
Array.prototype.some
Array.prototype.sort
- And above of typed arrays.
Examples of incorrect code for this rule:
/*eslint array-callback-return: "error"*/
var indexMap = myArray.reduce(function(memo, item, index) {
memo[item] = index;
}, {});
var foo = Array.from(nodes, function(node) {
if (node.tagName === "DIV") {
return true;
}
});
var bar = foo.filter(function(x) {
if (x) {
return true;
} else {
return;
}
});
Examples of correct code for this rule:
/*eslint array-callback-return: "error"*/
var indexMap = myArray.reduce(function(memo, item, index) {
memo[item] = index;
return memo;
}, {});
var foo = Array.from(nodes, function(node) {
if (node.tagName === "DIV") {
return true;
}
return false;
});
var bar = foo.map(node => node.getAttribute("id"));
Known Limitations
This rule checks callback functions of methods with the given names, even if the object which has the method is not an array.
When Not To Use It
If you don't want to warn about usage of return
statement in callbacks of array's methods, then it's safe to disable this rule.
Version
This rule was introduced in ESLint 2.0.0-alpha-1.