Assigning a Value to a Child Table Field in Frappe or ERPNext

When working with child tables in the Frappe Framework or ERPNext, some functionalities that work out of the box with other DocTypes that aren't child tables may prove to be a pain. In this tutorial, I will quickly brush through the following:

• How to listen to the add-row event in a child table
• How to assign a value to a field in a child table on adding a new row
• How to assign a value to a field in a child table on changing another field in the same child table

LISTENING TO THE ADD-ROW EVENT

frappe.ui.form.on('Article Details', {
    form_render: function(frm,cdt,cdn) {
       let item = locals[cdt][cdn]; 
       let articleId = Math.round(+new Date()/1000);
       item.article_id = articleId;
       frm.refresh_field('my_article');
    },
});

LISTENING TO A CHANGE IN ANOTHER FIELD IN THE SAME CHILD TABLE

frappe.ui.form.on("Article Details", "article_name", function(frm, cdt, cdn) {
    let item = locals[cdt][cdn]; 
    let articleId = Math.round(+new Date()/1000);
    item.article_id = articleId;
    frm.refresh_field('my_article');
});


Notice the presence of cdt and cdn in both functions .
That means that child doctype and child docname are passed to function and hence you can know what row was modified and triggered.
    locals is a global array that contains all the local documents opened by the user
    item is the row that the user is working with

https://youtu.be/4jpTLIPbW2Q