oberonjs/doc/wiki/compiler-options.md

checkIndexes option generates additional code to check ARRAY or STRING indexes at run-time.

Example:

var language = require("oberon/oberon_grammar.js").language;
var options = {checkIndexes: true};
result = require("oc.js").compile(
        source_code, 
        language, 
        errors_handler,
        options
        );