JavaScript post request like a form submit

Question

I'm trying to direct a browser to a different page. If I wanted a GET request, I might say

document.location.href = 'http://example.com/q=a';

But the resource I'm trying to access won't respond properly unless I use a POST request. If this were not dynamically generated, I might use the HTML

<form action="http://example.com/" method="POST">
  <input type="hidden" name="q" value="a">
</form>

Then I would just submit the form from the DOM.

But really I would like JavaScript code that allows me to say

post_to_url('http://example.com/', {'q':'a'});

What's the best cross browser implementation?

Edit

I'm sorry I was not clear. I need a solution that changes the location of the browser, just like submitting a form. If this is possible with XMLHttpRequest, it is not obvious. And this should not be asynchronous, nor use XML, so Ajax is not the answer.

Answer 1

this is the answer of rakesh, but with support for arrays (which is quite common in forms):

plain javascript:

function post_to_url(path, params, method) {
    method = method || "post"; // Set method to post by default, if not specified.

    // The rest of this code assumes you are not using a library.
    // It can be made less wordy if you use one.
    var form = document.createElement("form");
    form.setAttribute("method", method);
    form.setAttribute("action", path);

    var addField = function( key, value ){
        var hiddenField = document.createElement("input");
        hiddenField.setAttribute("type", "hidden");
        hiddenField.setAttribute("name", key);
        hiddenField.setAttribute("value", value );

        form.appendChild(hiddenField);
    }; 

    for(var key in params) {
        if(params.hasOwnProperty(key)) {
            if( params[key] instanceof Array ){
                for(var i = 0; i < params[key].length; i++){
                    addField( key, params[key][i] )
                }
            }
            else{
                addField( key, params[key] ); 
            }
        }
    }

    document.body.appendChild(form);
    form.submit();
}

oh, and here's the jquery version: (slightly different code, but boils down to the same thing)

function post_to_url(path, params, method) {
    method = method || "post"; // Set method to post by default, if not specified.

    var form = $(document.createElement( "form" ))
        .attr( {"method": method, "action": path} );

    $.each( params, function(key,value){
        $.each( value instanceof Array? value : [value], function(i,val){
            $(document.createElement("input"))
                .attr({ "type": "hidden", "name": key, "value": val })
                .appendTo( form );
        }); 
    } ); 

    form.appendTo( document.body ).submit(); 
}

Answer 2

A simple quick-and-dirty implementation of @Aaron answer:

document.body.innerHTML += '<form id="dynForm" action="http://example.com/" method="post"><input type="hidden" name="q" value="a"></form>';
document.getElementById("dynForm").submit();

Of course, you should rather use a JavaScript framework such as Prototype or jQuery...

Answer 3

Here is how I wrote it using jQuery. Tested in Firefox and Internet Explorer.

function postToUrl(url, params, newWindow) {
    var form = $('<form>');
    form.attr('action', url);
    form.attr('method', 'POST');
    if(newWindow){ form.attr('target', '_blank'); 
  }

  var addParam = function(paramName, paramValue) {
      var input = $('<input type="hidden">');
      input.attr({ 'id':     paramName,
                 'name':   paramName,
                 'value':  paramValue });
      form.append(input);
    };

    // Params is an Array.
    if(params instanceof Array){
        for(var i=0; i<params.length; i++) {
            addParam(i, params[i]);
        }
    }

    // Params is an Associative array or Object.
    if(params instanceof Object) {
        for(var key in params){
            addParam(key, params[key]);
        }
    }

    // Submit the form, then remove it from the page
    form.appendTo(document.body);
    form.submit();
    form.remove();
}

Answer 4

The easiest way is using Ajax Post Request:

$.ajax({
    type: "POST",
    url: 'http://www.myrestserver.com/api',
    data: data,
    success: success,
    dataType: dataType
    });

where:

• data is an object
• dataType is the data expected by the server (xml, json, script, text, html)
• url is the address of your RESt server or any function on the server side that accept the HTTP-POST.

Then in the success handler redirect the browser with something like window.location.

Answer 5

Yet another recursive solution, since some of others seem to be broken (I didn't test all of them). This one depends on lodash 3.x and ES6 (jQuery not required):

function createHiddenInput(name, value) {
    let input = document.createElement('input');
    input.setAttribute('type','hidden');
    input.setAttribute('name',name);
    input.setAttribute('value',value);
    return input;
}

function appendInput(form, name, value) {
    if(_.isArray(value)) {
        _.each(value, (v,i) => {
            appendInput(form, `${name}[${i}]`, v);
        });
    } else if(_.isObject(value)) {
        _.forOwn(value, (v,p) => {
            appendInput(form, `${name}[${p}]`, v);
        });
    } else {
        form.appendChild(createHiddenInput(name, value));
    }
}

function postToUrl(url, data) {
    let form = document.createElement('form');
    form.setAttribute('method', 'post');
    form.setAttribute('action', url);

    _.forOwn(data, (value, name) => {
        appendInput(form, name, value);
    });

    form.submit();
}

Answer 6

This is based on beauSD's code using jQuery. It is improved so it works recursively on objects.

function post(url, params, urlEncoded, newWindow) {
    var form = $('<form />').hide();
    form.attr('action', url)
        .attr('method', 'POST')
        .attr('enctype', urlEncoded ? 'application/x-www-form-urlencoded' : 'multipart/form-data');
    if(newWindow) form.attr('target', '_blank');

    function addParam(name, value, parent) {
        var fullname = (parent.length > 0 ? (parent + '[' + name + ']') : name);
        if(value instanceof Object) {
            for(var i in value) {
                addParam(i, value[i], fullname);
            }
        }
        else $('<input type="hidden" />').attr({name: fullname, value: value}).appendTo(form);
    };

    addParam('', params, '');

    $('body').append(form);
    form.submit();
}