This question already has answers here:
Clean way to keep original variable and destructure at the same time
(5 answers)
Closed 2 years ago.
I have the following function.
returnStateElement = (...elements) => {
const copy = Object.assign({}, this.state);
return elements.reduce((obj, key) => ({ ...obj, [key]: copy[key] }), {});
};
Working:
f = () => {
const dataSender = this.returnStateElement('email', 'password');
let { email, password } = dataSender;
console.log(dataSender,email,password);
}
Not working:
f2 = () => {
const { email, password } = dataSender = this.returnStateElement('email', 'password');
console.log(dataSender,email,password);
}
Is there a way to make a more compact type of assignment like f2()?
The following should work, you don't have to assign the results to an intermediate variable, you just need to provide the exact names that are in the returned object
f2 = () => {
const { email, password } = this.returnStateElement('email', 'password');
console.log(dataSender,email,password);
}
Example
const foo = () => {
return {
'a': '1',
'b': '2'
}
}
const bar = () => {
const { a, b } = foo();
console.log(a)
console.log(b)
}
bar();
// Logs 1, 2
f2 = () => {
const { email, password, ...rest } = this.returnStateElement('email', 'password');
console.log(email,password, rest);
// you can combine all like
console.log({...rest, email, password });
}
Related
I'm trying to understand behavior of function based composition in JavaScript.
const Animal = (name) => {
let properties = { name };
return ({
get name() { return properties.name },
set name(newName) { properties.name = newName },
breathe: function() {console.log(`${this.name} breathes!`); }
})
}
const aquaticKind = (animal) => ({
swim: () => console.log(`${animal.name} swims`)
})
const walkingKind = (animal, noOfLegs) => {
const properties = { noOfLegs }
return ({
get noOfLegs() { return properties.noOfLegs },
set noOfLegs(n) { properties.noOfLegs = n; },
walk: () => console.log(`${animal.name} walks with ${properties.noOfLegs} legs`)
})
}
const egglayingKind = (animal) => ({
layEgg: () => console.log(`${animal.name} laid an egg`)
})
const Crocodile = (name) => {
const info = Animal(name);
return Object.assign(info,
walkingKind(info, 4),
aquaticKind(info),
egglayingKind(info)
);
}
const snooty = Crocodile('snooty');
snooty.breathe();
snooty.swim();
snooty.walk();
snooty.name = "coolie";
snooty.noOfLegs = 23 // I expected this to get update to 23
snooty.swim();
snooty.walk();
snooty.layEgg();
If you run the code above, you will see that noOfLegs never get updated, while name get updated. I can't seem to wrap my head around this. How do we make noOfLegs get updated too?
MDN Documentation for object.assign shows you how to copy "accessors"
Here's your code that works as expected - the completeAssign function is based entirely on the code in that link
const completeAssign = (target, ...sources) => {
sources.forEach(source => {
const descriptors = Object.keys(source).reduce((descriptors, key) => {
descriptors[key] = Object.getOwnPropertyDescriptor(source, key);
return descriptors;
}, {});
Object.getOwnPropertySymbols(source).forEach(sym => {
const descriptor = Object.getOwnPropertyDescriptor(source, sym);
if (descriptor.enumerable) {
descriptors[sym] = descriptor;
}
});
Object.defineProperties(target, descriptors);
});
return target;
};
const Animal = (name) => {
const properties = { name };
return ({
get name() { return properties.name },
set name(newName) { properties.name = newName },
breathe () { console.log(`${this.name} breathes!`); }
})
}
const aquaticKind = (animal) => ({
swim: () => console.log(`${animal.name} swims`)
});
const walkingKind = (animal, noOfLegs) => {
const properties = { noOfLegs };
return ({
get noOfLegs() { return properties.noOfLegs },
set noOfLegs(n) { properties.noOfLegs = n; },
walk: () => console.log(`${animal.name} walks with ${properties.noOfLegs} legs`)
})
}
const egglayingKind = (animal) => ({
layEgg: () => console.log(`${animal.name} laid an egg`)
})
const Crocodile = (name) => {
const info = Animal(name);
return completeAssign(info,
walkingKind(info, 4),
aquaticKind(info),
egglayingKind(info)
);
}
const snooty = Crocodile('snooty');
snooty.breathe();
snooty.swim();
snooty.walk();
snooty.name = "coolie";
snooty.noOfLegs = 23;
snooty.swim();
snooty.walk();
snooty.layEgg();
This question already has answers here:
What is destructuring assignment and its uses?
(3 answers)
Closed 1 year ago.
Might sound complicated, but let me show you with code
const createCharacter = () => {
...
...
return [name, age];
};
const [userName, userAge] = createRefreshToken();
But I need to create the same userName and userAge variables when the function returns an object not an array
return { name, age };
or with the same variables' names
return { userName, userAge};
You can return an object from a function and destructure(Read) it with a new reference variable as
const { name: userName, age: userAge } = createCharacter();
const createCharacter = () => {
const name = "test Name",
age = 20;
// ...
// ...
return { name, age };
};
const { name: userName, age: userAge } = createCharacter();
console.log(userName);
console.log(userAge);
or You can create a new property when you return object from a function.
const createCharacter = () => {
const name = "test Name",
age = 20;
// ...
// ...
return { userName: name, userAge: age };
};
const { userName, userAge } = createCharacter();
console.log(userName);
console.log(userAge);
as you see the code, on the handleUpdateFilter function the second "if" some how defaultCourseData is filtered as filteredData of the first "if". Thank you for helping me!
setup() {
const course = ref();
const defaultCourseData = null
const gettingCourse = async () => {
const { data } = await getCourse();
defaultCourseData = data
course.value = data;
};
const handleUpdateFilter = (data) => {
// data is filtering value
if (data.value.view) {
const filteredData = defaultCourseData.sort((a, b) => b.luotXem - a.luotXem);
course.value = filteredData;
}
if (!data.value.view) {
course.value = defaultCourseData // This case some how defaultCourseData filtered too
}
};
onMounted(() => {
gettingCourse();
});
return {
course,
handleUpdateFilter,
defaultCourseData
};
},
Your defaultCourseData variable isn't reactive.
Therefore it should be evaluated as null at every call.
Try this
defineComponent({
setup() {
const course = ref([]);
const defaultCourseData = ref([]);
const gettingCourse = async () => {
const { data } = await getCourse();
defaultCourseData.value = data
course.value = data;
};
const handleUpdateFilter = (data) => {
// data is filtering value
if (data.value.view) {
course.value = defaultCourseData.value.sort((a, b) => b.luotXem - a.luotXem);
}
if (!data.value.view) {
course.value = defaultCourseData.value // This case some how defaultCourseData filtered too
}
};
onMounted(async () => {
await gettingCourse();
});
return {
course,
handleUpdateFilter,
defaultCourseData
};
})
Edit: The actual issue here was, that the defaultCourseData always returned a sorted array as Array.prototype.sort() mutates the Array.
So making a copy solves the issue.
if (data.value.view) { course.value = [...defaultCourseData.value].sort((a, b) => b.luotXem - a.luotXem); }
I have API query and getting the result and setting those in a state variable in Oncompleted method of API query, Now i am updating the same state variable in another api query "onCompleted method.
I am not able to access the result from state what i have set before in first api query and below is my code
Query 1:
const designHubQueryOnCompleted = designHubProject => {
if (designHubProject) {
const {
name,
spaceTypes
} = designHubProject;
updateState(draft => { // setting state here
draft.projectName = name;
draft.spaceTypes = (spaceTypes || []).map(po => {
const obj = getTargetObject(po);
return {
id: po.id,
name: obj.name,
category: obj.librarySpaceTypeCategory?.name,
description: obj.description,
warning: null // trying to modify this variable result in another query
};
});
});
}
};
const { projectDataLoading, projectDataError } = useProjectDataQuery(
projectNumber,
DESIGNHUB_PROJECT_SPACE_TYPES_MIN,
({ designHubProjects }) => designHubQueryOnCompleted(designHubProjects[0])
);
Query 2:
const {
// data: designhubProjectSpaceTypeWarnings,
loading: designhubProjectSpaceTypeWarningsLoading,
error: designhubProjectSpaceTypeWarningsError
} = useQuery(DESIGNHUB_PROJECT_LINKED_SPACETYPE_WARNINGS, {
variables: {
where: {
projectNumber: { eq: projectNumber }
}
},
onCompleted: data => {
const projectSpaceTypeWarnings = data.designHubProjectLinkedSpaceTypeWarnings[0];
const warnings = projectSpaceTypeWarnings.spaceTypeWarnings.reduce((acc, item) => {
const spaceTypeIdWithWarningState = {
spaceTypeId: item.spaceTypeProjectObjectId,
isInWarningState: item.isInWarningState
};
acc.push(spaceTypeIdWithWarningState);
return acc;
}, []);
console.log(state.spaceTypes); // trying to access the state here but getting empty array
if (state.spaceTypes.length > 0) {
const updatedSpaceTypes = state.spaceTypes;
updatedSpaceTypes.forEach(item => {
const spaceTypeWarning = { ...item };
spaceTypeWarning.warning = warnings?.filter(
w => w.spaceTypeId === spaceTypeWarning.id
).isInWarningState;
return spaceTypeWarning;
});
updateState(draft => {
draft.spaceTypes = updatedSpaceTypes;
});
}
}
});
Could any one please let me know where I am doing wrong with above code Or any other approach to modify the state, Many thanks in advance!!
what is the best practice to modify and return a new object from a function?
I wrote the following function :
export const addItemToCart = (currentCart, item) => {
const { name, ...otherProps } = item;
//if item exist in the cart
if (currentCart[name]) {
currentCart[name]["quantity"]++;
return currentCart;
}
//if the item does not exist
else
{
currentCart[name] = { ...otherProps };
currentCart[name]["quantity"] = 1;
return currentCart;
}
// the function must return a new modified object on each call
};
Obviously, the hard-coded property "quantity", and the return statements can definitely be improved.
how can I improve this function to be more readable?
More "readable" is very opinion-based, either way, you can try something like this:
const currentCart = {
hello: {
quantity: 1
}
};
const addItemToCart = (currentCart, item) => {
const { name } = item;
// Short circuit + return the last value
const quantityPrev = currentCart[name] && currentCart[name].quantity;
// Or operator on boolean expression
const quantity = 1 + (quantityPrev || 0);
// Destructing for shallow copy, dynamic key assign
return { ...currentCart, [name]: { quantity } };
};
console.log(addItemToCart(currentCart, { name: 'hello' }));
console.log(addItemToCart(currentCart, { name: 'blazer' }));