# \[vtk.js\] vtkLookupTable.setNumberOfTableValues is not a function
**URL:** https://discourse.vtk.org/t/vtk-js-vtklookuptable-setnumberoftablevalues-is-not-a-function/11453
**Category:** Support
**Tags:** vtkjs
**Created:** [May 15, 2023, 8:26am UTC](https://discourse.vtk.org/t/vtk-js-vtklookuptable-setnumberoftablevalues-is-not-a-function/11453 "2023-05-15T08:26:54Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [May 15, 2023, 8:26am UTC](https://discourse.vtk.org/t/vtk-js-vtklookuptable-setnumberoftablevalues-is-not-a-function/11453/1 "2023-05-15T08:26:54Z")
Hello
I’m trying to build a custom LUT, but I can’t translate one example from python/c++ to javascript. My code fails at the line vtkLookupTable.setNumberOfTableValues(256) saying that it is not a function.
What is wrong here?
```auto
function buildLookupTable(){
// Same colors as for 2D
const grad = ["#FFFAFA", "#FFEDD6", "#FFE1B2", "#FFD58E", "#FFC96B",
"#FFBD47", "#FFB123", "#FFA500", "#FF8D00", "#FF7500", "#FF5E00",
"#FF4600", "#FF2F00", "#FF1700", "#FF0000"];
// Build the color transfer function
let ctransfer = vtk.Rendering.Core.vtkColorTransferFunction.newInstance();
for (i = 0; i < grad.length; i++) {
let color = hexToRgbA(grad[i]);
ctransfer.addRGBPoint(i, ...color);
}
ctransfer.build();
// Build the lookup table with 256 colors and 1/5 transparent
let numberOfColors = 256;
let lut = vtk.Common.Core.vtkLookupTable.newInstance();
lut.setNumberOfTableValues(numberOfColors);
for (i = 0; i < numberOfColors; i++) {
let rgb = ctransfer.getColor( ((i * grad.length)/numberOfColors ) );
lut.setTableValue(i, rgb[0],rgb[1],rgb[1], Math.min(1, i*5/numberOfColors));
}
lut.setNanColor(1,0,1,0);
lut.build();
return lut;
}
```
Best regards
Alex
---
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [May 15, 2023, 9:49am UTC](https://discourse.vtk.org/t/vtk-js-vtklookuptable-setnumberoftablevalues-is-not-a-function/11453/2 "2023-05-15T09:49:34Z")
> [@Alex\_Vergara](#):
>
> `lut.setTableValue`
This is harder than I thought: setTableValue is also not a function!!
Is there a way to build a LookupTable in vtk.js??
---
### Author:  [@Alex\_Vergara](https://discourse.vtk.org/u/Alex_Vergara)
#### Post date: [May 15, 2023, 12:09pm UTC](https://discourse.vtk.org/t/vtk-js-vtklookuptable-setnumberoftablevalues-is-not-a-function/11453/3 "2023-05-15T12:09:18Z")
I found a way, although it is really odd and not as I expect the api to work
Final working example:
```auto
// grad is an array of string hex colors
function buildLookupTable(grad){
// Build the color transfer function
let ctransfer = vtk.Rendering.Core.vtkColorTransferFunction.newInstance();
for (i = 0; i < grad.length; i++) {
let rgb = hexToRgbA(grad[i]);
ctransfer.addRGBPoint(i, rgb[0], rgb[1], rgb[2]); // There is no way to add alpha here
}
ctransfer.build();
// Build the lookup table
let lut = vtk.Common.Core.vtkLookupTable.newInstance();
let numberOfColors = lut.getNumberOfColors(); // Default 256 colors
// Build the color table (returns as Float32Array)
let colorArray = ctransfer.getUint8Table(0,numberOfColors-1,numberOfColors,true); // true adds space for alpha channel
for (i = 0; i < numberOfColors/5; i++) { // 1/5 transparent with increased opacity
colorArray[i * 4 + 3] = i*5;
}
// Convert to vtkDataArray
let colorTable = vtk.Common.Core.vtkDataArray.newInstance({
name: "Color Data Array",
values: colorArray,
numberOfComponents: 4 // 4 components R, G, B, A
});
// Assign the table and build the lut
lut.setTable(colorTable);
lut.build();
return lut;
}
```