How to use the @antv/util/lib/is-string function in @antv/util

if (isObject(val)) {
            model[cfg] = clone(val);
          } else {
            model[cfg] = defaultModel[cfg];
          }
        }
      });
    }

    graph.emit('beforeadditem', { type, model });

    if(type === EDGE) {
      let source: string | Item = (model as EdgeConfig).source
      let target: string | Item = (model as EdgeConfig).target

      if (source && isString(source)) {
        source = graph.findById(source);
      }
      if (target && isString(target)) {
        target = graph.findById(target);
      }

      if (!source || !target) {
        throw new Error('The source or target node of edge ' + model.id + ' does not exist!')
        // console.warn('The source or target node of edge ' + model.id + ' does not exist!');
        // return;
      }

      item = new Edge({
        model,
        source,
        target,

public removeItem(item: Item): void {
    // 如果item是字符串，且查询的节点实例不存在，则认为是删除group
    let nodeItem = null;
    if (isString(item)) {
      nodeItem = this.findById(item);
    }

    if (!nodeItem && isString(item)) {
      this.get('customGroupControll').remove(item);
    } else {
      this.get('itemController').removeItem(item);
    }
  }

calculationGroupPosition() {
    const graph = this.graph;

    const nodes = graph.findAllByState('node', 'selected');

    let minx = Infinity;
    let maxx = -Infinity;
    let miny = Infinity;
    let maxy = -Infinity;

    // 获取已节点的所有最大最小x y值
    for (const id of nodes) {
      const element = isString(id) ? graph.findById(id) : id;
      const bbox = element.getBBox();
      const { minX, minY, maxX, maxY } = bbox;
      if (minX < minx) {
        minx = minX;
      }

      if (minY < miny) {
        miny = minY;
      }

      if (maxX > maxx) {
        maxx = maxX;
      }

      if (maxY > maxy) {
        maxy = maxY;

public setGroupStyle(keyShape: ShapeBase, style: string | object) {
    if (!keyShape || keyShape.get('destroyed')) {
      return;
    }
    let styles = {};
    const { hover: hoverStyle, default: defaultStyle } = this.styles;
    if (isString(style)) {
      if (style === 'default') {
        styles = deepMix({}, defaultStyle);
      } else if (style === 'hover') {
        styles = deepMix({}, hoverStyle);
      }
    } else {
      styles = deepMix({}, defaultStyle, style);
    }
    // tslint:disable-next-line:forin
    for (const s in styles) {
      keyShape.attr(s, styles[s]);
    }
  }

public updateLayout(cfg): void {
    const layoutController = this.get('layoutController');
    let newLayoutType;

    if (isString(cfg)) {
      newLayoutType = cfg;
      cfg = {
        type: newLayoutType
      };
    } else {
      newLayoutType = cfg.type;
    }

    const oriLayoutCfg = this.get('layout');
    const oriLayoutType = oriLayoutCfg ? oriLayoutCfg.type : undefined;

    if (!newLayoutType || oriLayoutType === newLayoutType) {
      // no type or same type, update layout
      const layoutCfg: any = {};
      Object.assign(layoutCfg, oriLayoutCfg, cfg);
      layoutCfg.type = oriLayoutType ? oriLayoutType : 'random';

public removeItem(item: Item): void {
    // 如果item是字符串，且查询的节点实例不存在，则认为是删除group
    let nodeItem = null;
    if (isString(item)) {
      nodeItem = this.findById(item);
    }

    if (!nodeItem && isString(item)) {
      this.get('customGroupControll').remove(item);
    } else {
      this.get('itemController').removeItem(item);
    }
  }

public setItemState(item: Item, state: string, enabled: boolean): void {
    if (isString(item)) {
      item = this.findById(item);
    }

    this.get('itemController').setItemState(item, state, enabled);
    this.get('stateController').updateState(item, state, enabled);
  }

export const formatPadding = (padding: IPadding): number[] => {
  let top = 0;
  let left = 0;
  let right = 0;
  let bottom = 0;

  if (isNumber(padding)) {
    top = left = right = bottom = padding;
  } else if(isString(padding)) {
    const intPadding = parseInt(padding, 10)
    top = left = right = bottom = intPadding;
  } else if (isArray(padding)) {
    top = padding[0];
    right = !isNil(padding[1]) ? padding[1] : padding[0];
    bottom = !isNil(padding[2]) ? padding[2] : padding[0];
    left = !isNil(padding[3]) ? padding[3] : right;
  }
  return [ top, right, bottom, left ];
}

private initCanvas() {
    let container: string | HTMLElement = this.get('container')
    if(isString(container)) {
      container = document.getElementById(container)
      this.set('container', container)
    }

    if(!container) {
      throw new Error('invalid container')
    }

    const width: number = this.get('width')
    const height: number = this.get('height')
    const pixelRatio: number = this.get('pixelRatio')

    const canvas = new GCanvas({
      container,
      width,
      height,