1) Write down the JavaScript code to enable the insertion of new buttons into the sequence at the particular situations.
2) Approximate the post fixed expression
a) Initialize an empty stack.
While there exist more symbols within postfix string
{
b) If token is an operand, push it onto the stack.
c) If token is an operator
{
d) Pop two topmost values from stack, and store them into the order t1, the topmost, and t2 the second value.
e) Determine the partial result within the following order t2 operator t1
f) Push the result of this calculation onto stack.