Nunjucks：異步自定義標簽不適用於版本> 2.3

Question

使用nunjucks版本3.2.0異步自定義標簽無效，但使用版本2.3.0則有效； 2.3.0以上的任何版本都不起作用。

parse ( parser, nodes, lexer ) { 
   let tok = parser.nextToken(); 
   let args = parser.parseSignature(null, true); 
   parser.advanceAfterBlockEnd(tok.value); 
   return new nodes.CallExtensionAsync(this, 'run', args); 
}

run ( context, args, callback ) { 
   setTimeout(() => { 
      let tag = "<div><h1>Title</h1></div>" 
      callback(null, new nunjucks.runtime.SafeString(tag)); 
    }, 2000); 
}

Answer 1

下面是如何在帶有異步加載器和標記的瀏覽器中使用nunjucks的方法。

import '/js/vendors/nunjucks.min.js';

// Define custom async loader
var MyLoader = nunjucks.Loader.extend({
    async: true,
    getSource: function(path, cb) {
        fetch('/templates/' + path)
            .then(res => res.text())
            .then(src => cb(null, {src, path, noCache: false}))
            .catch(cb);
    }
});

// Define environment with custom loader
var env = new nunjucks.Environment(new MyLoader(), {autoescape: true});

// Define custom tag "get" to load remote data by url to var
// Example: 
// {% get book = '/api/books/10' %}
// {{ book.id }} {{ book.name }}
function GetExtension(cb) {
    this.tags = ['get'];

    this.parse = function(parser, nodes, lexer) {
        var tok = parser.nextToken();
        var args = parser.parseSignature(null, true);
        parser.advanceAfterBlockEnd(tok.value);

        return new nodes.CallExtensionAsync(this, 'run', args, cb);
    };

    this.run = function(context, args, cb) {
        let ref = args instanceof Object && 
            Object.keys(args).filter(e => e != '__keywords')[0];
        var url = args[ref];
        var headers =  {pragma: 'no-cache', 'cache-control': 'no-cache'}

        fetch(url, {headers})
            .then(res => res.json())
            .then(function (res) {
                if (res.error)
                    console.error(url, res.error);

                context.ctx[ref] = res.error ? undefined : res;
                cb && cb();
            })
            .catch(cb);
    };
}

env.addExtension('GetExtension', new GetExtension());

// Example of async filter (similar to `include`-tag)
// Usage: {{ 'template-name.njk' | render({a: 10, text: 'OK'}) }}
env.addFilter('render', function (template, ctx, cb) {
    env.render(template, ctx, 
        (err, html) => cb && cb(err, !err ? env.filters.safe(html) : undefined)
    );
}, true);

// Example of sync filter
env.addFilter('time', function (datetime) {
    return new Date(+datetime).toLocaleTimeString([], {hour: '2-digit', minute:'2-digit'});
});

export {env as njk};