未捕获的TypeError：无法读取未定义的属性“state”

Question

我有以下功能：

extractCountries: function() {
    var newCountries = [];
    _.forEach(this.props.countries, function(country) {

        var monthTemp = Utils.thisMonthTemp(parseFloat(country["name"]["temperature"]));

        if(parseFloat(country["name"]["safety"]) > this.state.minSafety &&
           parseFloat(country["name"]["nature"]) > this.state.minNature &&
           this.state.weather.min <= monthTemp &&
           monthTemp <= this.state.weather.max) {

            newCountries.push(country);
        }
    }).bind(this);
    return newCountries;
  }

我在parseFloat(country["name"]["safety"]) > this.state.minSafety &&行：

Uncaught TypeError: Cannot read property 'state' of undefined

但是我绑定了外部React对象：

}).bind(this);

那么为什么会出现这种错误？

Answer 1

试试这个

extractCountries: function() {
        var newCountries = [];
        _.forEach(this.props.countries, function(country) {

            var monthTemp = Utils.thisMonthTemp(parseFloat(country["name"]["temperature"]));

            if(parseFloat(country["name"]["safety"]) > this.state.minSafety &&
               parseFloat(country["name"]["nature"]) > this.state.minNature &&
               this.state.weather.min <= monthTemp &&
               monthTemp <= this.state.weather.max) {

                newCountries.push(country);
            }
        }, this );
        return newCountries;
      }

Answer 2

如评论所述，您只需要这样做

extractCountries: function() {
    var newCountries = [];
    _.forEach(this.props.countries, function(country) {

        var monthTemp = Utils.thisMonthTemp(parseFloat(country["name"]["temperature"]));

        if(parseFloat(country["name"]["safety"]) > this.state.minSafety &&
           parseFloat(country["name"]["nature"]) > this.state.minNature &&
           this.state.weather.min <= monthTemp &&
           monthTemp <= this.state.weather.max) {

            newCountries.push(country);
        }
    }.bind(this));
    return newCountries;
  }