Filter through string that has to match an element of the array

     let variables= Object.keys(this.state.variables); //this contains an array like so ["aab","abb","acc"];
    const operations=["+","-","*","/",".","(",")"];
    const numbers=[0,1,2,3,4,5,6,7,8,9];
    let allOfThem=[...variables,...operations,...numbers];
    let checker = value =>allOfThem.some(element => value.includes(element));
newArr=string.split(""); // <= doesn't make sense, huh?    

I am not getting anything from the filter.

The main issue is the length of the variables I can split the string using .split("") because the variables have a length longer than 1.

What is your question?

I am not getting anything from the filter.

Looks like you are calling nested functions here. filter method only takes in a simple callback function that checks for conditionals.