Prefer that
for-in loops should include an if statement JS-0051
Anti-pattern
Minor
8 months ago
—
a year old
Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
957 delete attrs['aria-selected'];
958 }
959
960 for (var attr in attrs) { 961 var val = attrs[attr]; 962 963 option.setAttribute(attr, val); 964 } 965
966 if (data.children) {
967 var $option = $(option);Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
658 };
659
660 Utils._convertData = function (data) {
661 for (var originalKey in data) { 662 var keys = originalKey.split('-'); 663 664 var dataLevel = data; 665 666 if (keys.length === 1) { 667 continue; 668 } 669 670 for (var k = 0; k < keys.length; k++) { 671 var key = keys[k]; 672 673 // Lowercase the first letter 674 // By default, dash-separated becomes camelCase 675 key = key.substring(0, 1).toLowerCase() + key.substring(1); 676 677 if (!(key in dataLevel)) { 678 dataLevel[key] = {}; 679 } 680 681 if (k == keys.length - 1) { 682 dataLevel[key] = data[originalKey]; 683 } 684 685 dataLevel = dataLevel[key]; 686 } 687 688 delete data[originalKey]; 689 } 690
691 return data;
692 };Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
510
511 var methods = [];
512
513 for (var methodName in proto) { 514 var m = proto[methodName]; 515 516 if (typeof m !== 'function') { 517 continue; 518 } 519 520 if (methodName === 'constructor') { 521 continue; 522 } 523 524 methods.push(methodName); 525 } 526
527 return methods;
528 }Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
957 delete attrs['aria-selected'];
958 }
959
960 for (var attr in attrs) { 961 var val = attrs[attr]; 962 963 option.setAttribute(attr, val); 964 } 965
966 if (data.children) {
967 var $option = $(option);Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
658 };
659
660 Utils._convertData = function (data) {
661 for (var originalKey in data) { 662 var keys = originalKey.split('-'); 663 664 var dataLevel = data; 665 666 if (keys.length === 1) { 667 continue; 668 } 669 670 for (var k = 0; k < keys.length; k++) { 671 var key = keys[k]; 672 673 // Lowercase the first letter 674 // By default, dash-separated becomes camelCase 675 key = key.substring(0, 1).toLowerCase() + key.substring(1); 676 677 if (!(key in dataLevel)) { 678 dataLevel[key] = {}; 679 } 680 681 if (k == keys.length - 1) { 682 dataLevel[key] = data[originalKey]; 683 } 684 685 dataLevel = dataLevel[key]; 686 } 687 688 delete data[originalKey]; 689 } 690
691 return data;
692 };
Description
Looping over objects with a for in loop will include properties that are inherited through the prototype chain.
This behavior can lead to unexpected keys in your for loop.
Bad Practice
for (const key in foo) {
doSomething(key);
}
Recommended
for (const key in foo) {
if (Object.prototype.hasOwnProperty.call(foo, key)) {
doSomething(key);
}
}
for (const key of Object.keys(foo)) {
doSomething(key);
}