How to custom node with input execution

I has read the Custom Node Document , I want to write script to custom a node like UE4 DoOnce node,  here are my code

// -----JS CODE----- 
// @input execution void(string text) myInExec 
// @output execution void(string text) myOutExec 
if (script.myOutExec) { 
    script.myExec("here is text"); 
}

but I got this

I need custom node like DoOnce, thank you