Find a point on a line given a distance from a known point on the line

find_point_on_line.js

public findDistanceBetweenPoints(pointA, pointB) {
    var a = pointA["x"] - pointB["x"]
    var b = pointA["y"] - pointB["y"]
    var length = Math.sqrt(a*a + b*b)
    return length
}


public findSlope(pointA, pointB) {
    var a = pointB["y"] - pointA["y"]
    var b = pointB["x"] - pointA["x"]
    var m = a / b
    return m
}


public findUnitLengthVector(slope) {
    var mSquared = slope**2
    var unitLengthVector = Math.sqrt(1+mSquared)
    return unitLengthVector
}

public findClosestPoint(point1, point2, targetPoint) {
    var distance1 = this.findDistanceBetweenPoints(point1, targetPoint)
    var distance2 = this.findDistanceBetweenPoints(point2, targetPoint)

    if(distance1 < distance2){
        return point1
    }
    return point2
}

public findMissingCoordinate(pointA, pointB, distance){
    var slope = this.findSlope(pointA, pointB)
    var unitLengthVector = this.findUnitLengthVector(slope)

    var x1 = (pointA["x"] - (distance/unitLengthVector))
    var y1 = (pointA["y"] - (distance/unitLengthVector))

    var x2 = (pointA["x"] + (distance/unitLengthVector))
    var y2 = (pointA["y"] + (distance/unitLengthVector))

    var point1 = {"x": x1, "y": y1}
    var point2 = {"x": x2, "y": y2}

    return this.findClosestPoint(point1, point2, pointB)
}