[QUESTION] Updating a component type trait definition after init

Hello! you must attach a listener for the file property, so whenever it changes to a new value(file), your listener will append it to the end of the options:

            model: {
                defaults: {
                    ['selected-src']: '',
                    tagName: 'div',
                    resizable: true,
                    content: '<b>UPLOAD</b>',
                    traits: [
                        {
                            id: 'selected-src',
                            type: 'select',
                            label: 'file',
                            name: 'selected-src',
                            options: files,
                            changeProp: 1,
                        },
                    ]
                }
            },
            view: {
                init() {
                    this.listenTo(this.model, 'change:selected-src', this.doStuff)
                },
                doStuff() {
                    const trait = this.model.getTrait('selected-src')
                    const traitOptions = [{name: 'new file', value: 'new file url'}]
                    trait.set('options', [...trait.get('options'), ...traitOptions])
                },
            }

NOTICE here i am listening to the changes on the selected-src itself, for your case you must listen to your file related property. NOTICE i see that for your selected-src trait definition, you have not specified changeProp. if it is intentional then you are dealing with an attribute of the component and listener attachment would be like this: init() { this.listenTo(this.model, 'change:attributes:selected-src', this.doStuff)} cheers.

Yeah the key part proposed by @pouyamiralayi is here

const trait = this.model.getTrait('selected-src')
const traitOptions = [{name: 'new file', value: 'new file url'}]
trait.set('options', [...trait.get('options'), ...traitOptions])

This is how you update traits at run-time (more about this here)