My version of the checkForWin method before testing

/**
     * Method that checks if the last placed token produced a win
     * @param {Array} allSpaces - Contains the two dimensional array of alls spaces of the board
     * @param {Object} space - contains the space of the last played token
     */
    checkForWin(allSpaces, space) {
        const spaceColumn = space.x;
        const spaceRow = space.y;
        const player = space.owner;
        const spacesBelow = allSpaces[x].slice(y+1);
        const samePlayer = 0;
        const amountSpacesLEFT = allSpaces.length - space.x + 1;
        const amountSpacesRIGHT = space.y;

        //Check for vertical win
        for(let i = 0; i < spacesBelow.length; i += 1) {
            if(spacesBelow[spacesBelow.length-1 - i].owner === player){
                samePlayer += 1;
            } else {
                samePlayer = 0;
                break;
            } 
        }

        //Check for diagonal win in top left and bottom right directions
        for(let i = 0; i < amountSpacesLEFT;i += 1) {
            if(allSpaces[space.x-1-i][space.y+1+i].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        for(let i = 0; i < amountSpacesRIGHT;i += 1) {
            if(allSpaces[space.x+1+i][space.y-1-i].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        if (samePlayer >= 3) {
            alert(`${player.name} wins!`)
        } else {
            samePlayer = 0;
        }

        //Check for diagonal win in top right and bottom left directions
        for(let i = 0; i < amountSpacesLEFT;i += 1) {
            if(allSpaces[space.x-1-i][space.y-1-i].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        for(let i = 0; i < amountSpacesRIGHT;i += 1) {
            if(allSpaces[space.x+1+i][space.y+1+i].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        if (samePlayer >= 3) {
            alert(`${player.name} wins!`)
        } else {
            samePlayer = 0;
        }

        //Checks for horizontal
        for(let i = 0; i < amountSpacesLEFT;i += 1) {
            if(allSpaces[space.x-1-i][space.y].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        for(let i = 0; i < amountSpacesRIGHT;i += 1) {
            if(allSpaces[space.x+1+i][space.y].owner === player){
                samePlayer += 1;
            } else {
                break;
            } 
        }

        if (samePlayer >= 3) {
            alert(`${player.name} wins!`)
        } else {
            samePlayer = 0;
        }
        }