I want to duplicate one array of objects into multiple ones, because every one of them I need to use in separate places.
if(!this.tempLookups){
for (let count = 0; count < this.dates.length; count++) {
this.tempLookups[count] = this.lookups[key];
}
}
Error: Uncaught (in promise) TypeError: Cannot set property '0' of null
The actual reason for the error is clearly in error message that you are trying to set the property for a null. So in order to fix simply define it after the if.
if(!this.tempLookups){
his.tempLookups = [];
for (let count = 0; count < this.dates.length; count++) {
this.tempLookups[count] = this.lookups[key];
}
}
You can do it in a single line without a for loop using Array#fill method since you are filling with the same value.
if(!this.tempLookups){
this.tempLookups = new Array(this.dates.length).fill(this.lookups[key]);
}
You can do this like this:
if (!this.tempLookups) {
this.tempLookups = [];
for (let i = 0; i < this.dates.length; i++) {
this.tempLookups.push(Array.from(this.lookups[key]));
}
}
Note that the this.tempLookups variable is initialized as empty array before we start inserting data. The Array.from call in for loop makes sure we actually create (shallow) copies of the this.lookups[key] array, instead of just assigning reference to the same this.lookups[key] array multiple times. Without Array.from changing one array would change all of them - because in reality there would be only one array referenced multiple times.
this.tempLookups = []after the if conditionthis.tempLookups = new Array(this.dates.length).fill(this.lookups[key])this.lookups[key]an array?this.lookupsis array of arrays, than you should useArray.fromto create shallow copy ofthis.lookups[key]array - see my answer.