"this.mapHeaders is not a function"

[tjconcept]

• Operating System: macOS 10.13.6
• Node Version: 10.11.0
• NPM Version: 6.4.1
• csv-parser Version: 2.0.0

Expected Behavior

$ echo "a
> 1" | csv-parser
{"a": "1"}

Actual Behavior

$ echo "a
> 1" | csv-parser
/Users/tj/.npm-config/lib/node_modules/csv-parser/index.js:70
        const newHeader = this.mapHeaders({ header, index })
                               ^

TypeError: this.mapHeaders is not a function
    at headers.forEach (/Users/tj/.npm-config/lib/node_modules/csv-parser/index.js:70:32)
    at Array.forEach (<anonymous>)
    at CsvParser._compile (/Users/tj/.npm-config/lib/node_modules/csv-parser/index.js:69:20)
    at CsvParser._online (/Users/tj/.npm-config/lib/node_modules/csv-parser/index.js:181:12)
    at CsvParser._transform (/Users/tj/.npm-config/lib/node_modules/csv-parser/index.js:242:16)
    at CsvParser.Transform._read (_stream_transform.js:190:10)
    at CsvParser.Transform._write (_stream_transform.js:178:12)
    at doWrite (_stream_writable.js:410:12)
    at writeOrBuffer (_stream_writable.js:394:5)
    at CsvParser.Writable.write (_stream_writable.js:294:11)

How Do We Reproduce?

$ echo "a
> 1" | csv-parser

[shellscape]

Not sure what scenario would cause this. Our tests don't reflect that, and I'm unable to reproduce using your example. Line 29 in the v2.0.0 tag source (which you're running) sets the options and asserts that mapHeaders cannot be undefined

csv-parser/index.js

Line 26 in 97edb38

if (Array.isArray(opts)) opts = { headers: opts }

which is then set on line 37 to the instance

csv-parser/index.js

Line 37 in 97edb38

this[key] = options[key]

, and line 69 is using an arrow function

csv-parser/index.js

Line 69 in 97edb38

this.headers.forEach((header, index) => {

sothis is from the same scope as the previous line, on which this.headers exists.

Probably something you're going to have to investigate on your end and submit a patch or PR for.

[tjconcept]

What? It's right here:

csv-parser/bin/csv-parser

Line 73 in 2c95c35

mapHeaders: argv.remove ? mapHeaders : null,

[shellscape]

Sweet. Please open a PR and we'll merge your fix.

[tjconcept]

I don't have a fix. I have no idea what that code does.

How could yours work? I suppose that's the key to the bug.

[dimfeld]

It looks like bin/csv-parser wasn't updated for the breaking changes in version 2.

[shellscape]

Happy to merge and publish a PR to fix. Just don't have the time to triage for another week or so.

[tjconcept]

It looks like bin/csv-parser wasn't updated for the breaking changes in version 2.

There must be something else (or more) at play.

I'm unable to reproduce using your example

I think @shellscape should first triage this so we fully understand the bug before attempting a fix.

[dimfeld]

The root of the problem appears to be where the defaults are merged with the passed-in options.

csv-parser/index.js

Line 29 in 2c95c35

const options = Object.assign({}, defaults, opts)

where the default and options merge used to be a more manual process performed in a way that would not treat falsy values for the map* functions as valid arguments. (Below code is from the v1.12.1 tag)

csv-parser/index.js

Line 32 in d8791d3

this.mapHeaders = opts.mapHeaders || identity

The most obvious fix to me is to just revert back to the old option-parsing code, maybe just for the map functions. If that sounds ok to you, I can probably submit a PR some time this week. bin/csv-parser also needs its mapHeaders arguments updated.

[tjconcept]

I agree with that analysis, but that doesn't explain why @shellscape is not able to reproduce it. I think that should be debugged first.

[shellscape]

(On a plane right now and the wifi is miraculously working)

It might be a sticky global bin. My first step in every issue is to try and reproduce locally. If it's unreproducible for me, but reproducible for a bunch of others, then it's probably a wonk on my end. I wouldn't give my lack of reproduction much credence until I've got the time to investigate.

I wouldn't recommend a reversion as a fix, but rather trying to get the new style to party correctly with the breaking changes in the major.

[scottp]

Part of this may be to do with documentation error. The documentation on NPM shows

      .pipe(csv(
        {
          mapHeader: function(header, index) {

But the actual code is

      .pipe(csv(
        {
          mapHeaders: function(header, index) {

[shellscape]

Commit a22f006 resolves this. (Github looks to be having issues tonight)