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HTML

              
                <canvas id="canvas" width="300" height="400" />
              
            
!

CSS

              
                body {
  padding: 20px;
  background: #eee;
}
#canvas {
  border: 1px solid #ccc;
}
              
            
!

JS

              
                function findBreakPoint (text, width, context) {
    var min = 0;
    var max = text.length - 1;
     
    while (min <= max) {
        var middle = Math.floor((min + max) / 2);
        var middleWidth = context.measureText(text.substr(0, middle)).width;
        var oneCharWiderThanMiddleWidth = context.measureText(text.substr(0, middle + 1)).width;
        if (middleWidth <= width && oneCharWiderThanMiddleWidth > width) {
            return middle;
        }
        if (middleWidth < width) {
            min = middle + 1;
        } else {
            max = middle - 1;
        }
    }
     
    return -1;
}
function breakLinesForCanvas (text, width, font) {
    var canvas = document.getElementById('canvas');
    var context = canvas.getContext('2d');
    var result = [];
    var breakPoint = 0;
     
    if (font) {
        context.font = font;
    }
     
    while ((breakPoint = findBreakPoint(text, width, context)) !== -1) {
        result.push(text.substr(0, breakPoint));
        text = text.substr(breakPoint);
    }
     
    if (text) {
        result.push(text);
    }
     
    return result;
}

var result = breakLinesForCanvas('使用很寻常的二分查找,如果某一个位置之前的文字宽度小于等于设定的宽度,并且它之后一个字之前的文字宽度大于设定的宽度,那么这个位置就是文本的换行点。上面只是找到一个换行点,对于输入的一段文本,需要循环查找,直到不存在这样的换行点为止, 完整的代码如下', 300, '16px 微软雅黑');
console.log(result);

var lineHeight = 30;
var context = document.getElementById('canvas').getContext('2d');
context.font = "16px 微软雅黑";

result.forEach(function (line, index) {
  context.fillText(line, 0, lineHeight * index + 30);
});

              
            
!
999px

Console