Source contract and expected records
This is an original, fully synthetic mapping example. Inputs are plain, acyclic JSON-shaped records with the fields shown; the canonical shape and rejection codes belong to this example. Adapt the contract before using a different source.
This local source stores line objects under positive integer slot keys written without leading zeros. Each line has an item label and a nonnegative safe integer quantity. Sort by numeric slot and retain the original slot on the output. Missing positions create no record. Empty slots produces an empty list.
| Case | Input record (JSON) | Expected output (JSON) |
|---|---|---|
| Keep source slots | {"slots":{"1":{"item":"A","units":0},"3":{"item":"C","units":2}}} | {"ok":true,"value":{"lines":[{"slot":1,"item":"A","units":0},{"slot":3,"item":"C","units":2}]}} |
| Reject negative quantity | {"slots":{"1":{"item":"A","units":-1}}} | {"ok":false,"error":"SLOT_LINE"} |
| Preserve empty slots | {"slots":{}} | {"ok":true,"value":{"lines":[]}} |
Run the local transformation
Run the complete example as a JavaScript module in Node.js. It contains the pure mapping function, all three inputs and literal expected outputs; assertions stop on a mismatch. A rejected case returns ok=false with an error code, rather than a partial canonical record.
import assert from 'node:assert/strict';
function repeatingSlots(i){
const fail=error=>({ok:false,error});if(!i||!i.slots||typeof i.slots!=='object'||Array.isArray(i.slots))return fail('SLOT_OBJECT');
const lines=[];
for(const [key,r]of Object.entries(i.slots)){
const slot=Number(key);if(!/^[1-9]\d*$/.test(key)||!Number.isSafeInteger(slot))return fail('SLOT_POSITION');
if(!r||typeof r.item!=='string'||!r.item||!Number.isSafeInteger(r.units)||r.units<0)return fail('SLOT_LINE');
lines.push({slot,item:r.item,units:r.units});
}
lines.sort((a,b)=>a.slot-b.slot);return {ok:true,value:{lines}};
}
// Original synthetic cases; expected outputs are literal records.
const cases = [
{
"label": "Keep source slots",
"input": {
"slots": {
"1": {
"item": "A",
"units": 0
},
"3": {
"item": "C",
"units": 2
}
}
},
"expected": {
"ok": true,
"value": {
"lines": [
{
"slot": 1,
"item": "A",
"units": 0
},
{
"slot": 3,
"item": "C",
"units": 2
}
]
}
}
},
{
"label": "Reject negative quantity",
"input": {
"slots": {
"1": {
"item": "A",
"units": -1
}
}
},
"expected": {
"ok": false,
"error": "SLOT_LINE"
}
},
{
"label": "Preserve empty slots",
"input": {
"slots": {}
},
"expected": {
"ok": true,
"value": {
"lines": []
}
}
}
];
for (const sample of cases) {
const actual = repeatingSlots(sample.input);
assert.deepEqual(actual, sample.expected);
console.log(sample.label, JSON.stringify(actual));
}
Work through the boundary
Slots 1 and 3 exist. Should a blank line be inserted for slot 2?
Show the worked answer
No. Output is slot 1 with A=0, then slot 3 with C=2. The gap is preserved, while the explicitly supplied zero line remains.