Combining json

[prashasti-k]

There is a union of arrays but how can I combine objects or add a key-value to an object using expressions?
I want something like
math.evaluate('merge(obj, { newKey: newValue }))', { obj: {a:1}, newValue: 3 })
So that this replicates the spread operator as well like { ...obj, newKey: newValue}

[josdejong]

You can write a merge function yourself and import it in your mathjs instance. There is indeed no built in solution for this (yet). If there is enough interest, we can look into implementing the spread operator ... in the expression parser. I like it a lot in Javascript :).