如果将代码移到属性更改处理程序中，而不是视图的onRender函数中，您将能够根据需要使用API调用中的值。
检查此小更改：https://jsfiddle.net/jvas28/8sb3tn94/1/

const editor = grapesjs.init({
    container: '#gjs',
  fromElement: 1,
  height: '100%',
  storageManager: { type: 0 },
});

editor.DomComponents.addType('test-component', {
    model: {
        defaults: {
            testprop: '12345',
            url: 'https://jsonplaceholder.typicode.com/posts/1'
        },
        init() {
            console.log('Local hook: model.init', this.attributes.testprop);
            fetch(this.attributes.url)
                .then(response => response.json())
                .then(commits => {
                    this.set('testprop', 'Test');
                    console.log(this.attributes.testprop);
                });
            this.listenTo(this, 'change:testprop', this.handlePropChange);
            // Here we can listen global hooks with editor.on('...')
        },
        updated(property, value, prevValue) {
            console.log('Local hook: model.updated',
                'property', property, 'value', value, 'prevValue', prevValue);
        },
        removed() {
            console.log('Local hook: model.removed');
        },
        handlePropChange() {
             let prop = this.get('testprop');
            // Here inside view it is getting the old value. of "testprop" i.e '12345' but not 
            //the new value 
            //which is being fetched from server in the init() of model.
            let comp1 = '<div>' +
                '<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Image_created_with_a_mobile_phone.png/1200px-Image_created_with_a_mobile_phone.png" />' +
                '<span title="foo">' + prop + '</span>' +  '</div>';

                const component = editor.addComponents(comp1);
            return component
        }
    },
    view: {
        init() {
            console.log('Local hook: view.init');
        },
       
    },
});

// A block for the custom component
editor.BlockManager.add('test-component', {
    label: 'Test Component',
    content: `<div data-gjs-type="test-component"></div>`,
});