Create a new binding and assign it the value undefined.
In these examples, a Binding is an object {value:mixed, mutable:Boolean, deletable:Boolean, initialized:Boolean}
Code: (Meta Ecma)
function CreateMutableBinding(N, D){ var envRec = this; if (!(N in envRec)) return; // "assert envRec does not already have a binding for N" envRec[N].value = {value:undefined, mutable:true, deletable:D, initialized:false}; };