please help with .$set data on vue , after read docs of vuejs.org I did not realize what must be index in $set when my data is already null and also syntax I need to write. please provide the syntax need for set data in this specific example. thank you.
//in vue js components:
data() {
return {
columnDefs: null
};
computed: {
onLoadColumns() {
// some logic here (manipulate received props from parent)
// logic bring this [{},{},{}]
// sth = [{},{},{}]
// now want to .$set() , (or maybe $add()) that array to data obj for reactivity.
// what syntax look like? this below didn't work.
this.$set(this.columnsDef, 0, sth);
}
You have a typo: should be this.$set(this.columnDef, 0, sth);. Not this.columnsDef - without s.
Also try to init you columnDef with [] in data:
data() {
return {
columnDefs: []
}
},
Or set empty array right before assigning to zero index:
this.columnDef = []
this.$set(this.columnDef, 0, sth)
Related
I have this object of arrays that I'm tryin to watch every update of.
myData = {
"299":[527],
"376":[630,629]
}
I read this documentation on watching an object which instructed to use either this.$set(object, propertyName, value) or Object.assign({}, this.object, dataToBeAppended) to watch an object. I used this.$set.
export default {
...
data() {
return {
myData: {},
};
},
watch: {
myData(newVal) {
console.log(`🔴localStorage`);
},
},
methods: {
onFoldChange(propertyName) {
const newArr = [...]
this.$set(this.myData, propertyName, newArr);
},
}
}
Unlike what I expected, vue captures changes on property only. Changes in value to an existing property are not being watched. For example, if a property "299" was newly added, it will print 🔴localStorage. When the value of a property "299" is updated from [527] to something else, nothing is fired. When I print myData, I see every value updated correctly. It is just that watch isn't capturing the changes.
The documentation also described we can watch an array using this.$set(this.myData, indexOfItem, newValue) so I also tried array version of the above code, like this.
this.$set(this.myData[propertyName], index, newValueToAdd);
This time it doesn't listen at all. Not even the first entry.
Is there any better way to solve this issue? How do others watch an object? Is the complication coming from the type of values (array) ?
Currently, myData watcher observes only an object. Object contains pointers to arrays as in JS Objects & Arrays are passed by reference not by copy. That's why it can detect only changes in keys and with simple values. If you want to observe it deeper - I mean also those subarrays (or subobjects) - just use deep watch.
watch: {
myData: {
deep: true,
handler (newVal) {
console.log(`🔴localStorage`);
}
}
}
Another possible solution could be to use some Array.prototype operation to modify an array if it already exists. E.g:
methods: {
onFoldChange(propertyName) {
if (propertyName in this.myData && Array.isArray(this.myData[propertyName])) {
this.myData[properyName].push(162) // Some random value
} else {
const newArr = [...]
this.$set(this.myData, propertyName, newArr);
}
},
}
I am trying to update a single property of an object from an array using vuex.
here is my code in store file.
export default{
namespaced: true,
state: {
customers: null,
},
mutations: {
UPDATE_MODIFIED_STATE(state, value) {
state.customers = [
...state.customers.filter(item => item.Id !== value.Id),
value,
];
},
},
And below code is from my .vue file.
export default {
computed: {
customerArray() {
return this.$store.state.CustomerStore.customers;
},
},
methods: {
...mapMutations('CustomerStore', ['UPDATE_MODIFIED_STATE']),
updateCustomers() {
if(someCondition) {
this.customerArray.forEach((element) => {
element.IsModified = true;
this.UPDATE_MODIFIED_STATE(element);
});
}
/// Some other code here
},
},
};
As you can see I want to update IsModified property of object.
It is working perfectly fine. it is updating the each customer object.
Just want to make sure, is it correct way to update array object or I should use Vue.set.
If yes, I should use Vue.set, then How can I use it here.
You are actually not mutating your array, what you do is replacing the original array with a new array generated by the filter function and the passed value. So in your example there is no need to use Vue.set.
You can find more information about replacing an array in the vue documentation.
The caveats begin however when you directly set an item with the index or when you modify the length of the array. When doing this the data will no longer be reactive, you can read more about this here.
For example, consider the following inside a mutation:
// If you update an array item like this it will no longer be reactive.
state.customers[0] = { Id: 0, IsModified: true }
// If you update an array item like this it will remain reactive.
Vue.set(state.customers, 0, { Id: 0, IsModified: true })
I had an API call to the backend and based on the returned data, I set the reactive data dynamically:
let data = {
quantity: [],
tickets: []
}
api.default.fetch()
.then(function (tickets) {
data.tickets = tickets
tickets.forEach(ticket => {
data.quantity[ticket.id] = 0
})
})
Based on this flow, how can I set watcher for all reactive elements in quantity array dynamically as well?
You can create a computed property, where you can stringify the quantity array, and then set a watcher on this computed property. Code will look something like following:
computed: {
quantityString: function () {
return JSON.stringify(this.quantity)
}
}
watch: {
// whenever question changes, this function will run
quantityString: function (newQuantity) {
var newQuantity = JSON.parse(newQuantity)
//Your relevant code
}
}
Using the [] operator to change a value in an array won't let vue detect the change, use splice instead.
I need to check variable rasters_previews_list for changing. Here is my code:
var userContent = Vue.extend({
template: '<p>Some template</p>',
data: function () {
return {
rasters_previews_list: []
}
},
watch: {
'rasters_previews_list': function(value, mutation) {
console.log("Value changed");
}
}
});
But In console I do not see Value changed when it got new data.
Data changing function:
map.on('draw:created', function (e) {
//...
Vue.http.post('/dbdata', DataBody).then((response) => {
userContent.rasters_previews_list = response; // putting JSON answer to Component data in userContent
console.log(response);
}, (response) => {
console.log("Can't get list rasters metadata from DB. Server error: ", response.status)
});
I change value in map.on('draw:created', function (e) (Leaflet JS). I see console.log output, so seems data is changing.
If you want to change the value of an array you will have to use the special Array extension methods Vue.set and Vue.delete.
Due to limitations of JavaScript, Vue cannot detect the following changes to an Array:
When you directly set an item with the index, e.g. vm.items[0] = {};
When you modify the length of the Array, e.g. vm.items.length = 0.
https://vuejs.org/api/#Vue-set
This problem is also mentioned in the common gotchas
When you modify an Array by directly setting an index (e.g. arr[0] = val) or modifying its length property. Similarly, Vue.js cannot pickup these changes. Always modify arrays by using an Array instance method, or replacing it entirely. Vue provides a convenience method arr.$set(index, value) which is just syntax sugar for arr.splice(index, 1, value).
I'm not really understanding where to put function() { return {} } and where not to when it comes to deeply nesting computed properties.
By the way, this is in a component!
computed: {
styles: function() {
return {
slider: function() {
return {
height: {
cache: false,
get: function() {
return 'auto';
}
},
width: {
cache: false,
get: function() {
return $('#slideshow').width();
}
}
}
}
}
}
},
This is returning undefined. When I get rid of the function() { return {} } inside of the slider index, it returns an object when I do styles.slider.width instead of the get() return. It just shows an object with cache and get as indexes..
Thanks for any help!
The reason I'm asking is because I have multiple nested components that involve styling from the parent. Slider, tabs, carousels, etc. So I wanted to organize them like this.
I believe you mean to return a computed object, but not actually structure the computation in a nested manner?
What the others have said regarding the 'computed' hook not having syntax for nesting is correct, you will likely need to structure it differently.
This may work for you: I generate many objects in a similar fashion.
computed: {
computedStyles(){
var style = {slider:{}}
style.slider.height = 'auto'
style.slider.width = this.computedSlideshowWidth
return style
},
computedSlideshowWidth(){
return $('#slideshow').width()
}
As per 2020 and Vue 2.6.12 this is completelly possible. I believe this has been possible since v.2 but cannot confirm.
Here is the working example:
this.computed = {
// One level deep nested,
// get these at `iscomplete.experience`
// or `iscomplete.volume`
iscomplete: function() {
return {
experience: this.$data.experience !== null,
volume: this.$data.volume > 100,
// etc like this
};
},
// More levels deep nested.
// Get these at `istemp.value.v1 and `istemp.value.v2`
istemp: function() {
return {
value1: {
v1: this.$data.experience,
v2: 'constant'
}
}
}
};
As a result you will be able to access your deep nested computed in your template as e.g. follows <span v-text="iscomplete.experience"></span> that will output <span>true</span> for the first example computed above.
Note that:
Since Vue v.2 cache key is deprecated;
Vue would not execute functions assigned to a computed object nested keys;
You cannot have computed for non-Vue-reactive things which in your case is e.g. $('#slideshow').width(). This means they are not going to be re-computed on their content change in this case (which is a computed's sole purpose). Hence these should be taken away from computed key.
Other than that I find nested computeds to be quite helpful sometimes to keep things in better order.