Javascript 我不能把数字加在一起，尽管我使用了parseFloat，但我仍然得到了NaN

我不能把数字加在一起，尽管用了parseFloat，我还是得到了NaN.

本代码;

        console.log(freshsnow_single_resort.fs_ski_resort_aa_advanced_length);
        console.log(freshsnow_single_resort.fs_ski_resort_aa_expert_length);
        console.log(freshsnow_single_resort.fs_ski_resort_aa_freeride_length);
        console.log(freshsnow_single_resort.fs_ski_resort_aa_extreme_length);
        
        let fs_ski_resort_aa_advanced_length    = parseFloat(freshsnow_single_resort.fs_ski_resort_aa_advanced_length) 
        let fs_ski_resort_aa_expert_length      = parseFloat(freshsnow_single_resort.fs_ski_resort_aa_expert_length)
        let fs_ski_resort_aa_freeride_length    = parseFloat(freshsnow_single_resort.fs_ski_resort_aa_freeride_length)
        let fs_ski_resort_aa_extreme_length     = parseFloat(freshsnow_single_resort.fs_ski_resort_aa_extreme_length);
        
        let expert_km = parseFloat(fs_ski_resort_aa_advanced_length + fs_ski_resort_aa_expert_length + fs_ski_resort_aa_freeride_length + fs_ski_resort_aa_extreme_length);
        
        console.log(typeof fs_ski_resort_aa_advanced_length );
        console.log(typeof fs_ski_resort_aa_expert_length );
        console.log(typeof fs_ski_resort_aa_freeride_length );
        console.log(typeof fs_ski_resort_aa_extreme_length );
        
        console.log( expert_km );

在控制台中生成以下内容:

4901.39
2057.49
0
<<blank/novalue

Number
Number
Number
Number
NaN

我不明白发生了什么.如有任何帮助，不胜感激.