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Viewswhat is difference between using delete keyword , assign undefined value to object literal in javascript?
I met some needs for deep copying original object literals, excepts some keys. I know spread operator doesn't copy deeply whole nested objects, however it's not main points for this question, so let's pass that issues.
so, back in original question, I see no difference between using delete keyword and assign undefined to target property which I want to remove.
const original = {
a: 1,
b: 2,
}
const copied = {
...original,
b: undefined
}
const explicitDelete = {
...original
}
delete explicitDelete["b"]
seems copied way is less verbose, but it's totally okay with that way?
3 answers
Answer question0
I see no difference between using
deletekeyword and assignundefinedto target property
The difference is that the property still exists with the value undefined:
"b" in copied // true
"b" in explicitDelete // false
If you don't like the verbosity of delete, you can use a helper function
function omit(obj, ...keys) {
const res = {};
for (const p in obj)
if (!key.includes(p))
res[p] = obj[p];
return res;
}
omit(orignal, "b")
or object destructuring with rest syntax:
const {b:_, ...withoutB} = original;
See also How to omit specific properties from an object in JavaScript, How do I remove a property from a JavaScript object?, How can I clone a JavaScript object except for one key?.
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There is definitely a difference. When you use delete, the object will no longer have the property name at all. The in operator will indicate that. Setting the property value to undefined will not have that effect.
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delete removes the entry, that's the difference
