Feature: array & objects are difficult to handle

[BQXBQX]

When i write some demo for expr, i meet a problem:
If you don't use register to define your own functions and only use template syntax, it is difficult to handle arrays and objects.Here is an example:

const spec = {
        type: 'line',
        height: 400,
        width: 540,
        legend: false,
        y: 300,
        encode: {
            x: 'name',
            y: 'value'
        },
        scale: {
            y: {
                independent: true
            }
        },
        labels: [{
            text: '{a.value}',
           // here is the problem, how to filter this array 🤔
            selector: '{a}',
        }, ],
        axis: {
            y: {
                position: 'right',
                grid: null,
            },
        },
    },
}

I want to filter only the data of a certain index in the labels selector, but it is difficult to handle using only template syntax.

[BQXBQX]

Solution

1. While using expr to provide template capabilities, open a way to get register capabilities for your developers
2. We will extend a plugin to provide some array and object processing toolkits that are safer and more suitable for expr template syntax. This toolkit can be provided by us as a dependent package, which can be optionally integrated without increasing the size of the core code.

[hustcc]

I don't think it's necessary to consider, the selector itself has a simplified string enum value syntax.

[hustcc]

Reference: https://tedboy.github.io/jinja2/templ14.html

data | map(type="sports")