Cascade operator

[mindplay-dk]

I couldn't find this request in the issue backlog, so I'd like to request support for method and property cascades, e.g. via the .. operator, familiar from other languages like Dart.

While this is merely syntactic sugar, it's very convenient - take the following example:

function request(method: string, url: string, body?: string) : Promise<XMLHttpRequest> {
    return new Promise<XMLHttpRequest>(function (resolve, reject) {
        var xhr = new XMLHttpRequest()

        xhr.open(method, url)

        xhr.onload = function () {
            if (this.status >= 200 && this.status < 300) {
                resolve(xhr)
            } else {
                reject(xhr)
            }
        }

        xhr.onerror = function () {
            reject(new Error(`unable to complete ${method} request for: ${url}`))
        }
        
        xhr.send(body)
    })
}

We can discard the intermediary variable and references to it, so the above becomes:

function request(method: string, url: string, body?: string) : Promise<XMLHttpRequest> {
    return new Promise<XMLHttpRequest>(function (resolve, reject) {
        new XMLHttpRequest()
            ..open(method, url)
            ..onload = function () {
                if (this.status >= 200 && this.status < 300) {
                    resolve(xhr)
                } else {
                    reject(xhr)
                }
            }
            ..onerror = function () {
                reject(new Error(`unable to complete ${method} request for: ${url}`))
            }
            ..send(body)
    })
}

Dart having a very similar syntax, I believe this feature can basically be referenced 1:1 from Dart?

[aluanhaddad]

Duplicate of #8536