使用正则表达式进行匹配，如果配置位置对应的索引在数组中没有给出则以？替代

// 定义函数 
var template = function(template, txtArray) {
    return template.replace(/\$\{([1-9][0-9]*)\}/g, function(match,idx){
        var _index = parseInt(idx);
        if(txtArray[_index-1]) {
            return txtArray[_index-1];
        }else{
            return '?';
        }
    })
};

// 测试代码
console.log(template('hello ${1}, ${2} is the best ${3}', ['Miss Li', 'WildBerry', 'food']));
console.log(template('${1} + ${2} = ${3}', [2, 3, 5]));
console.log(template('${2}, ${4}, ${6}, ${12} ', [1,2,3,4,5,6,7,8]));