How to define a hash with enum keys in Typescript

I'm making a RAM Machine emulator in TypeScript, so I made an enum of the instruction types that a RAM can have:

enum InsType {
    LOAD,   // Put value from specified register (or literal) into accumulator.
    STORE,  // Store value from accumulator into specified register.
    READ,   // Read from input tape and write into specified register.
    WRITE,  // Write to output tape from specified register.
    ADD,    // Add value into accumulator.
    SUB,    // Subtract value from accumulator.
    MUL,    // Multiply accumulator by referenced (or literal) value.
    DIV,    // Divide accumulator by referenced (or literal) value.
    HALT,   // Stop program execution.
    JUMP,   // Jump unconditionally to line specified by tag.
    JZERO,  // Jump to line specified by tag if accumulator value is zero.
    JGTZ,   // Jump to line specified by tag if acc value is greater than zero.
}

I have to make sure each instruction has a valid operand type. My way of defining the valid operands is like this:

var valid_operands = {
  LOAD:   [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  STORE:  [                    OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  READ:   [                    OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  WRITE:  [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  ADD:    [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  SUB:    [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  MUL:    [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  DIV:    [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  HALT:   [OpType.NONE],
  JUMP:   [OpType.NAME],
  JZERO:  [OpType.NAME],
  JGTZ:   [OpType.NAME],
}

But I find that the TypeScript 'compiler' doesn't care what I put in the key values-- I can change LOAD: to LOADXYZ: and it won't bat an eye.

Also, when I try to change it to this:

var valid_operands = {
  InsType.LOAD:   [OpType.NUM_LITERAL, OpType.NUM_DIRECT, OpType.NUM_INDIRECT],
  ...

It warns ':' expected at line XX col YY (those being the position of the .). I'm using the Atom TypeScript plugin to work, if it helps. Any help is appreciated.