then there's no child with that name of that parent at the time your code executes.
ie, check the parent, check the name and check your timing.
i have parent and childs, and every one have name, i put instans name in the Animate and when i try to get it at console, its return null. when i do it with this["mcName"] its work...
show the code that works and the code just above or below that line that fails.
console.log(this.mymc.getChildByName("mc1")); // return null
console.log(this.mymc.["mc1"]); // return the mc
if you did everything correctly (with mymc on stage and mc1 a child of mymc), you would get nothing working until you removed that dot after mymc in console.log(this.mymc.["mc1"]);
you would then see
console.log(this.mymc.getChildByName("mc1")); //returns object
//does not work
console.log(this.mymc["mc1"]); // returns undefined
i can upload fla to this forum?