也来写个JSONP好了

[ghost]

带Promise的话后续操作感觉更顺，请斧正：

ES6：

'use strict';
!function() {
let JSONP = function(url, {data, callback} = {}) {
    let args = Object(data);
    let index = JSONP.counter++;
    let script = document.createElement('script');
    let queryStrings = Object.getOwnPropertyNames(args)
        .map(key => key + '=' + encodeURIComponent(args[key]))
        .concat(['callback=' + encodeURIComponent(`JSONP[${index}]`)]);
    let promise = new Promise(function(resolve, reject) {
        Object.defineProperty(JSONP, index, {
            writable: false,
            configurable: true,
            value: resolve
        });
        script.onerror = reject;
    });
    let head = document.head;
    let onload = () => (script.onload = script.onreadystatechange = null, head.removeChild(script));
    let scrUrl = String(url);
    script.src = scrUrl + (-1 === scrUrl.indexOf('?') ? '?' : '&') + queryStrings.join('&');        
    script.onload = onload;
    script.onreadystatechange = () => /loaded|complete/.test(script.readyState) && onload();
    head.appendChild(script);
    return promise
        .then(response => (delete JSONP[index], response))
        .then(response => 'function' === typeof callback ? callback(response) : response)
        .catch(error => console.warn(error));
};
JSONP.counter = 0;
return window.JSONP = JSONP;
}();

jQuery：

'use strict';
!function() {
    var JSONP = function(url, descriptor) {
        descriptor = Object(descriptor);
        url = String(url);
        var data = descriptor.data;
        var callback = descriptor.callback;
        var args = Object(data);
        var index = JSONP.counter++;
        var script = document.createElement('script');
        var queryStrings = [];
        var promise = new jQuery.Deferred();
        var head = document.head;
        var hasOwnProperty = Object.prototype.hasOwnProperty;
        var onload = function() {
            script.onload = script.onreadystatechange = null;
            return head.removeChild(script);
        };
        for(var key in args) {
            if(hasOwnProperty.call(args, key)) {
                queryStrings.push(key + '=' + encodeURIComponent(args[key]));
            }
        }
        queryStrings.push('callback=' + encodeURIComponent('JSONP[' + index + ']'));
        JSONP[index] = function(response) {
            delete JSONP[index];
            return promise.resolve('function' === typeof callback ? callback(response) : response);
        };
        script.src = url + (-1 === url.indexOf('?') ? '?' : '&') + queryStrings.join('&');
        script.onerror = promise.reject;
        script.onload = onload;
        script.onreadystatechange = function() {
            return /loaded|complete/.test(this.readyState) && onload();
        };
        head.appendChild(script);
        return promise.fail(function(error) {
            return console.warn(error);
        });
    };
    JSONP.counter = 0;
    return window.JSONP = JSONP;
}();

[island205]

'use strict'; 写在应该写在函数内部