How to write an interpreter for this in javascript?

Question

I want to write an interpreter for a scripting language in javascript. Something that could run this script:

set myVariable to "Hello World"
repeat 5 times with x
begin
    set myVariable to myVariable plus " " plus x
end
popup "myVariable is: " plus myVariable

Equivalent javascript above:

var myVariable = "Hello World";
for (var x=1; x<=5; x++) {
    myVariable += " " + x;
}
alert("myVariable is: " + myVariable);

I do not want to translate from one to another, I want to write a javascript program to interpret and execute the script directly. How can I do that?

Update:

I am looking for a tutorial (preferably in javascript, but C will do) that will guide me through this. I think I'm looking for one that doesn't use any external tools, since the tools seem to be my problem. I do not want to use something that calls libraries and a bunch of ready-made code. I want to see everything that has been done from scratch.

Answer 1

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: http://en.wikipedia.org/wiki/Compiler

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http://www.google.com/search?q=javascript+parser+generator

PEG.js - Parser JavaScript

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Answer 2

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Answer 3

Many of the answers you get are focused on the analytic part of creating an appraiser. See Programming Languages: An Application and Interpretation for Processing Writing Semantics for a Language.