genArrrayInstanceTests.scala

def genArrayInstanceTests(tree: LinkedClass): js.Tree = {
  import Definitions._
  import TreeDSL._

  implicit val pos = tree.pos

  val className = tree.name.name
  val displayName = decodeClassName(className)

  val objParam = js.ParamDef(Ident("obj"), rest = false)
  val obj = objParam.ref

  val depthParam = js.ParamDef(Ident("depth"), rest = false)
  val depth = depthParam.ref

  val createIsArrayOfStat = {
    envFieldDef("isArrayOf",
                className,
                js.Function(List(objParam, depthParam), className match {
                  case Definitions.ObjectClass =>
                    val dataVarDef = genLet(Ident("data"), mutable = false, {
                      obj && (obj DOT "$classData")
                    })
                    val data = dataVarDef.ref
                    js.Block(dataVarDef, js.If(!data, {
                      js.Return(js.BooleanLiteral(false))
                    }, {
                      val arrayDepthVarDef =
                        genLet(Ident("arrayDepth"), mutable = false, {
                          (data DOT "arrayDepth") || js.IntLiteral(0)
                        })
                      val arrayDepth = arrayDepthVarDef.ref
                      js.Block(arrayDepthVarDef, js.Return {
                        // Array[A] </: Array[Array[A]]
                        !js.BinaryOp(JSBinaryOp.<, arrayDepth, depth) &&
                        (// Array[Array[A]] <: Array[Object]
                          js.BinaryOp(JSBinaryOp.>, arrayDepth, depth) ||
                          // Array[Int] </: Array[Object]
                          !genIdentBracketSelect(data DOT "arrayBase",
                                                 "isPrimitive"))
                      })
                    }))

                  case _ =>
                    js.Return(! (! ({
                      genIsScalaJSObject(obj) && ((
                        obj DOT "$classData" DOT "arrayDepth") === depth) &&
                      genIsClassNameInAncestors(
                          className,
                          obj DOT "$classData" DOT "arrayBase" DOT "ancestors")
                    })))
                }))
  }
  val createAsArrayOfStat =
    if (semantics.asInstanceOfs == Unchecked) {
      js.Skip()
    } else {
      envFieldDef("asArrayOf",
                  className,
                  js.Function(List(objParam, depthParam), js.Return {
                    js.If(js.Apply(envField("isArrayOf", className),
                                   List(obj, depth)) || (obj === js.Null()), {
                            obj
                          }, {
                            genCallHelper(
                                "throwArrayCastException",
                                obj,
                                js.StringLiteral("L" + displayName + ";"),
                                depth)
                          })
                  }))
    }

  js.Block(createIsArrayOfStat, createAsArrayOfStat)
}

Original https://github.com/scala-js/scala-js/blob/29e46c2284afd48dcfe2dcacbcfe9f9fdbadf617/tools/shared/src/main/scala/org/scalajs/core/tools/linker/backend/emitter/ScalaJSClassEmitter.scala#L584

val newColumn =
  tok.length + 
  (if (split == Newline) newIndent
  else column + split.length)