I want to make an array based on two arrays - "ideaList" and "endorsements" declared globally. As ideaList and endorsements are used in other parts of the program I need them to be immutable, and I thought that .map and .filter would keep this immutability.
function prepareIdeaArray(){
var preFilteredIdeas=ideaList
.filter(hasIdeaPassedControl)
.map(obj => {obj.count = endorsements
.filter(x=>x.ideaNumber===obj.ideaNumber)
.reduce((sum, x)=>sum+x.count,0);
obj.like = endorsements
.filter(x=>x.ideaNumber===obj.ideaNumber && x.who===activeUser)
.reduce((sum, x)=>sum+x.count,0)===0?false:true
obj.position = generatePosition(obj.status)
obj.description = obj.description.replace(/\n/g, '<br>')
return obj;});
preFilteredIdeas.sort(compareOn.bind(null,'count',false)).sort(compareOn.bind(null,'position',true))
return preFilteredIdeas;
}
However, when I console.log ideaList after this function has been executed, I remark that objects of the array all have the "count", "like", "position" properties with values, which proves that the array has been mutated.
I tried by using .map only, but same result.
Would you know how I could prevent ideaList to get mutated? Also I would like to avoid to use const, as I declare ideaList globally first, and then assign to it some data in another function.