How Viscosity decides

For every array that holds object literals, Viscosity answers three questions, in order.

1. Is it a collection?

The array must be created once (const xs = [] or an array literal of object literals). Its records must be added with push({...}) or appear in the literal, and every record must have the same fields in the same order.

2. Is it safe?

Every use of the array and of its elements must be one Viscosity can rewrite:

allowed	refused (with the reason shown in explain)
xs.length, xs.push({...})	other methods: xs.map, xs.sort, …
xs[i].f, xs[i].f = v, xs[i].f += v	an element passed to a function, stored, returned, or compared with ===
const p = xs[i]; p.f	adding a property the records don’t have
for (const p of xs)	the array passed to unknown code or exported
passing xs to a function whose every caller passes xs	the variable reassigned

3. Will it pay off?

• At least one loop must read or write fields.
• The estimated (or profiled) size must reach --min-size (default 64).
• Fields that provably always hold numbers become Float64Array columns. Other fields become plain array columns, which hold any value exactly as before. If no field is numeric, there is nothing to gain and the collection is left alone.

Accesses that a loop doesn’t prove in bounds get a check that throws the same TypeError the original code would have (see Bounds).