use flask's url_for in javascript

js_routes.html

{% autoescape false %}
(function(){
var ruleMap = {{ rule_map }};
X = X || {};
X.url_for = function(endpoint, params) {
    var re = /\<\s*(\w+:)*(\w+)\s*\>/ig;

    if (!params) {
        params = {};
    }

    if (!ruleMap[endpoint]) {
        throw('endpoint is not exist: ' + endpoint);
    }
    var anchor = null;
    var base = "";

    if(params['_external']){
        base = "{{ web_host }}";
        delete params['_external'];
    }
    if(params['_anchor']){
        anchor = "#"+params['_anchor'];
        delete params['_anchor'];
    }

    var rules = ruleMap[endpoint];
    var url = null;
    var errors = [];
    $.each(rules, function(){
        var rule = this;
        var used_params = {};
        var unbuildable = false;

        var path = rule.replace(re, function (_i, _0, _1) {
            if (params.hasOwnProperty(_1)) {
                used_params[_1] = params[_1];
                return encodeURIComponent(params[_1]);
            } else {
                errors.push(_1 + ' does not exist in params for: '+rule);
                unbuildable = true;
            }
        });
        if(unbuildable || url) {
            return;
        }

        var query_string = '';

        for (var k in params) {
            if (used_params.hasOwnProperty(k)) {
                continue;
            }
            var v = params[k];
            if (query_string.length > 0) {
                query_string += '&';
            }
            query_string += encodeURIComponent(k) + '=' + encodeURIComponent(v);
        }
        url = path;
        if (query_string.length > 0) {
            url += '?' + query_string;
        }
    });
    if(!url){
        throw(errors.join(", "))
    }

    if(anchor){
        url = url+anchor;
    }
    return base+url;
}
X.url_for.rules = ruleMap;
})();
{% endautoescape %}

route.py

    @route("/routes.js", methods=["GET"])
    def js_routes(self):
        from flask import current_app, render_template
        import simplejson as json

        rule_map = defaultdict(list)

        for rule in current_app.url_map.iter_rules():
            rule_map[rule.endpoint].append(rule.rule)

        content = render_template("js_routes.html", {'rule_map':json.dumps(rule_map), 'web_host':config.get('WEB_HOST'))})
        return Response(
            content,
            content_type='text/javascript; charset=UTF-8',
            headers={
                'Cache-Control': 'no-cache',
            }
        )

usage.js

X.url_for('app.my_awesome_route', {id: 5, _external=True}) //make external url

/*
This requires jquery, but can easily not, since it just uses $.each in there
*/