Formula

Formulas are dynamic document properties that can be set on the fields.

Forumlas are defined as javascript functions and are called whenever any property of the document is updated using the set method, or just before inserting or updating the document.

Example:

module.exports = {
    name: "FormulaExample"
    fields: [
        {
            fieldtype: "Float",
            fieldname: "a"
        },
        {
            fieldtype: "Float",
            fieldname: "b"
        }
        {
            fieldtype: "Float",
            fieldname: "c",
            formula: doc => doc.a + doc.b
        }
    ]
}

Formula on child tables:

In child tables, both the parent and the child records are passed.

Example:

{
    fieldname: "amount",
    fieldtype: "Float",
    formula: (row, doc) => row.qty * row.rate
}

Sequence:

All child tables are executed first and all fields are executed in the sequence as defined in the DocType.

Fetching Values:

You can use the getFrom function to fetch values from another document.

Example:

{
    "fieldname": "rate",
    "label": "Rate",
    "fieldtype": "Currency",
    formula: (row, doc) => row.rate || doc.getFrom('Item', row.item, 'rate')
}

Async:

Formulas are evaluated as promises, so you can either directly return a value or a Promise.