how to access an object when the key is a string js code example

Example: object notation string javascript\

function getValueFromNotation(obj: Object,is: string|any[], value: any = undefined) {
    
    if (typeof is == 'string')
      return getValueFromNotation(obj,is.split('.'), value);
    else if (is.length==1 && value!==undefined)
      return obj[is[0]] = value;
    else if (is.length==0)
      return obj;
    else
      return getValueFromNotation(obj[is[0]],is.slice(1), value);
  
}