Finds closest value in sorted array

closestPoint.js

function closestPoint(arr, point){
    if(!Array.isArray(arr)) return [];
    point = Number.isFinite(point) ? point : 0;
    let prevDiff = Infinity;
    let result = arr.findIndex((value,key) => {
        let diff = Math.abs(value - point);
        return diff >= prevDiff ? true : (prevDiff = diff, false);
    });
    result = result === -1 ? arr.length - 1 : result - 1;
    return {key: result, value: arr[result]};
}
/// Examples of usage
closestPoint([10,20,30,40,50,60,70,80,90,100]) /// expected: {key:0, value:10}
closestPoint([10,20,30,40,50,60,70,80,90,100],50) /// expected: {key:4, value:50}
closestPoint([10,20,30,40,50,60,70,80,90,100],-1000) /// expected: {key:0, value:10}
closestPoint([10,20,30,40,50,60,70,80,90,100],1000) /// expected: {key:9, value:100}