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What is the difference between for..in and for each..in statements in javascript? Are there subtle difference that I don't know of or is it the same and every browser has a different name for it?
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foreach is useful when iterating all of the items in a collection. for is useful when iterating overall or a subset of items. The foreach iteration variable which provides each collection item, is READ-ONLY, so we can't modify the items as they are iterated. Using the for syntax, we can modify the items as needed.
each differs for the arguments passed to the callback. If you use _. forEach , the first argument passed to the callback is the value, not the key.
forEach is almost the same as for or for..of , only slower. There's not much performance difference between the two loops, and you can use whatever better fit's the algorithm. Unlike in AssemblyScript, micro-optimizations of the for loop don't make sense for arrays in JavaScript.
The forEach() method calls a function for each element in an array. The forEach() method is not executed for empty elements.
"for each...in" iterates a specified variable over all values of the specified object's properties.
Example:
var sum = 0;
var obj = {prop1: 5, prop2: 13, prop3: 8};
for each (var item in obj) {
sum += item;
}
print(sum); // prints "26", which is 5+13+8
Source
"for...in" iterates a specified variable over all properties of an object, in arbitrary order.
Example:
function show_props(obj, objName) {
var result = "";
for (var i in obj) {
result += objName + "." + i + " = " + obj[i] + "\n";
}
return result;
}
Source
Note 03.2013, for each... in loops are deprecated. The 'new' syntax recommended by MDN is for... of.
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